A 26-year-old American from Pennsylvania was beheaded to avenge the abuse of Iraqi prisoners by U.S. soldiers, and the militants who killed him videotaped the crime and posted it on a radical Islamic Web site.

Al Qaeda terrorist Abu Musab al-Zarqawi (search), believed to be behind the wave of homicide bombings in Iraq, may have either authorized the execution or actually performed the act himself, U.S. officials believe.

The video shows five men wearing headscarves and black ski masks standing behind a bound man in an orange jumpsuit similar to a prisoner's uniform. The prisoner identified himself on the video as Nick Berg (search), a 26-year-old Philadelphia native. His body was found near a highway overpass in Baghdad on Saturday, the same day he was beheaded, a U.S. official said.

"My name is Nick Berg, my father's name is Michael, my mother's name is Susan," the man says on the video. "I have a brother and sister, David and Sarah. I live in ... Philadelphia."

The video then cuts to Berg sitting on the floor, his hands tied behind his back, flanked by the masked men, as a statement is read in Arabic. Berg sits still during the statement, facing the camera, occasionally raising his shoulders.

After the statement, one assailant takes a large knife from under his clothing while another pulls Berg onto his side. The tape shows assailants thrusting the knife through his neck. A scream sounds before the men cut Berg's head off, repeatedly shouting "Allahu Akbar!" — or "God is great."

They then hold the head out before the camera.

The video is of poor quality, and its time stamp seems to show an 11-hour lapse between when the assailants finish their statement and push Berg down, to when they behead him. That suggests a delay between those two portions of tape posted on the Web site.

The FBI is analyzing the Internet video, said an official speaking on condition of anonymity, adding that it was too early to draw any conclusions.

"To see this poor soul beheaded is gruesome and barbaric," former U.S. Navy Judge Advocate Gen. Tim Susanin told Fox News. "We're really seeing the difficulty our troops are dealing with. They've now been infiltrated by members of Al Qaeda."

Berg's family said Tuesday they knew their son had been decapitated, but didn't know the details of the killing. When told of the video by an Associated Press reporter, Berg's father and his two siblings hugged and cried.

"I knew he was decapitated before. That manner is preferable to a long and torturous death. But I didn't want it to become public," Michael Berg said.

Berg was a small-business owner who went to Iraq as an independent businessman to help rebuild communication antennas, his family said Tuesday. Friends and family said he was a "free spirit" who wanted to help others — working in Ghana, in one example — and that his going to Iraq fit with that ideology. They said he supported the Iraqi war and the Bush administration.

The Bush administration said those who beheaded Berg would be hunted down and brought to justice.

"This shows the true nature of the people who are opposed to freedom and democracy in the region," White House Press Secretary Scott McClellan said. "Those who carried out this crime will be pursued and brought to justice."

But Michael Berg lashed out at the U.S. military and Bush administration, saying his son might still be alive if he had been allowed to leave the country on March 30, as he had originally planned.

"I think a lot of people are fed up with the lack of civil rights this thing has caused," he said. "I don't think this administration is committed to democracy."

Presumptive Democratic presidential nominee Sen. John Kerry of Massachusetts issued the following statement about the beheading:

"Like all Americans, I'm horrified and deeply saddened by the senseless murder of Nicholas Berg. My thoughts and prayers are with his family and with the families of all our troops and civilians working under such dangerous conditions to rebuild and bring peace to Iraq. We are grateful for the work you do and the risks you take. The terrorists who committed this atrocity will not prevail, and America stands together against them."

And on Capitol Hill Tuesday, lawmakers reacted to the videotaped beheading with shock, outrage and disgust.

"It's terrible. It's tragic," said Sen. John McCain, R-Ariz., who serves on the Senate Armed Services Committee. "These people have no regard for humanity."

"They're despicable in every way," said Sen. Lindsey Graham, R-S.C., also a member of the committee. "The challenge is to keep the fight going."

U.S. officials had feared the shocking photographs of U.S. soldiers abusing and humiliating Iraqis at Abu Ghraib prison west of Baghdad would endanger the lives of American troops and civilians.

Also, Berg's killing happened amid a climate of anti-Western sentiment, which flared in Iraq after last month's crackdown on Shiite extremists and the three-week Marine siege of Fallujah west of Baghdad. Anger at the United States swelled with the publication of the Abu Ghraib photographs, which continue to stir rage throughout the Arab world.

In the video, the executioner reads the following statement:

"For the mothers and wives of American soldiers, we tell you that we offered the U.S. administration to exchange this hostage with some of the detainees in Abu Ghraib (search) and they refused.

"So we tell you that the dignity of the Muslim men and women in Abu Ghraib and others is not redeemed except by blood and souls. You will not receive anything from us but coffins after coffins ... slaughtered in this way."

The video bears the title "Abu Musab al-Zarqawi shown slaughtering an American." It is unclear whether al-Zarqawi — a lieutenant of Usama bin Laden — is shown in the video, or is claiming responsibility for ordering the execution. Al-Zarqawi also is sought in the assassination of a U.S. diplomat in Jordan in 2002.

The Web site on which the video was posted is that of Muntada Al-Ansar, known as a clearinghouse for Al Qaeda and Islamic extremist groups' statements and tapes. An audiotape purportedly from bin Laden — which the CIA said was probably authentic — appeared on the same Web site last week.

Western officials say al-Zarqawi, whose real name is Ahmad Fadhil al-Khalayleh, is a lieutenant of bin Laden. The United States has offered $10 million for information leading to the capture or killing of al-Zarqawi, saying he is trying to build a network of foreign militants in Iraq to work for Al Qaeda.

In the video, the speaker threatened both President Bush and Pakistani President Gen. Pervez Musharraf (search).

"As for you Bush ... expect severe days. You and your soldiers will regret the day you stepped into the land of Iraq," he said. He described Musharraf as "a traitor agent."

The slaying recalled the kidnapping and videotaped beheading of Wall Street Journal reporter Daniel Pearl (search) in 2002 in Pakistan. Four Islamic militants have been convicted of kidnapping Pearl, but seven other suspects — including those who allegedly slit his throat — remain at large.

The Bergs, who live the Philadelphia suburb of West Chester, Pa., last heard from their son April 9, the same day insurgents attacked a U.S. convoy west of the capital.

Berg attended Cornell, Drexel, the University of Pennsylvania and the University of Oklahoma, where he got involved in rigging electronics equipment while working for the maintenance department, his father said. He helped set up equipment at the Republican National Convention in Philadelphia in 2000.

While at Cornell, he traveled to Ghana to teach villagers how to make bricks out of minimal material. His father said Berg returned from Ghana emaciated because he gave away most of his food and that the only possessions he had when he returned were the clothes on his back.

Michael Berg said his son saw his trip to Iraq as an adventure that also fit with his desire to help others.

"I would say he was a free spirit, very intelligent," said Nick Fillioe, a sports director at the West Chester YMCA. "He was a real smart guy. He knew a little bit about everything."

Berg's family said they were informed by the State Department on Monday that he was found dead.

When told about the Web site, Berg's father, brother and sister grasped one another and slowly dropped to the ground in their front yard, where they wept quietly while holding each other.

"I knew he was decapitated before," Michael Berg said. "That manner is preferable to a long and torturous death. But I didn't want it to become public."

Last month, Iraqi militants videotaped the killing of Italian hostage Fabrizio Quattrocchi, but the Arab TV network Al-Jazeera refused to air it because it was too graphic.

In the video of Berg, the executioners said they had tried to trade him for prisoners at Abu Ghraib.

"For the mothers and wives of American soldiers, we tell you that we offered the U.S. administration to exchange this hostage for some of the detainees in Abu Ghraib and they refused," one of the men read from a statement.

"So we tell you that the dignity of the Muslim men and women in Abu Ghraib and others is not redeemed except by blood and souls. You will not receive anything from us but coffins after coffins ... slaughtered in this way."

Berg's mother, Suzanne Berg of West Chester, Pa., said her son was in Iraq as an independent businessman to help rebuild communication antennas. He had been missing since April 9, she said.

"He had this idea that he could help rebuild the infrastructure," she said.

The U.S. military Tuesday said an American civilian was found dead in Baghdad, but did not release his identity. State Department spokeswoman Susan Pittman said she couldn't release the name of the dead American, but said she not aware of more than one civilian found dead in recent days.

The military said there were signs of trauma to the body. Suzanne Berg said she was told her son's death was violent but did not want to discuss details.

Berg, who was in Baghdad from late December to Feb. 1, returned to Iraq in March. He didn't find any work and planned again to return home on March 30, but his daily communications home stopped on March 24. He later told his parents he was jailed by Iraqi officials at a checkpoint in Mosul.

"He was arrested and held without due process," his father, Michael Berg, told the Daily Local News of West Chester recently. "By the time he got out the whole area was inflamed with violence.

The FBI on March 31 interviewed Berg's parents in West Chester. Jerri Williams, a spokeswoman for the Philadelphia FBI office, told The Philadelphia Inquirer the agency had been "asked to interview the parents regarding Mr. Berg's purpose in Iraq."

On April 5, the Bergs filed suit in federal court in Philadelphia, contending that their son was being held illegally by the U.S. military. The next day Berg was released. He told his parents he hadn't been mistreated.

The Bergs last heard from their son April 9, when he said he would come home by way of Jordan, Turkey or Kuwait. But by then, hostilities in Iraq had escalated.

The day Berg last made contact with his family also was the day that seven American contractors working for a subsidiary of Halliburton Corp. and two military men disappeared after their supply convoy was attacked on the outskirts of Baghdad.

Four of the Halliburton workers and one of the military men have since been confirmed dead. Halliburton worker Thomas Hamill escaped his captors May 2 and returned home to Mississippi on Saturday. The two other Halliburton workers and the other soldier remain missing.

Two soldiers also vanished April 9. One was later found dead and the other, Pfc. Keith M. Maupin of Batavia, Ohio, was taken captive and remains missing.

Suzanne Berg on Tuesday said she was told her son's body would be transported to Kuwait and then to Dover, Del. She said the family had been trying for weeks to learn where their son was but that federal officials had not been helpful.

"I went through this with them for weeks," she said. "I basically ended up doing most of the investigating myself."

The Associated Press contributed to this report.