Family members of an American and a Briton held by kidnappers in Iraq appealed for their lives after a grisly video posted on the Internet purportedly showed militants beheading U.S. civil engineer Eugene Armstrong (search) and threatening to kill another hostage in 24 hours.

The nine-minute tape, whose authenticity could not be verified, showed a sobbing, blindfolded man identified as Armstrong kneeling in front of five militants dressed in black. The banner of Al Qaeda ally Abu Musab al-Zarqawi's (search) Tawhid and Jihad hung on the wall behind them in the video posted Monday.

The man in the center read a statement, then pulled a knife, grabbed the hostage seated at his feet and sliced his head off. The victim screamed and blood poured from his neck. The alleged Jordanian terror mastermind purportedly conducted the beheading himself.

In an earlier video, Tawhid and Jihad had threatened to kill Armstrong, fellow American Jack Hensley and Briton Kenneth Bigley— all construction contractors — unless Iraqi women are released from two American prisons here.

The U.S. military says women are not held at Abu Ghraib (search) and Umm Qasr (search) prisons, but has acknowledged it is holding two female "security prisoners" elsewhere. They include Dr. Rihab Rashid Taha, a scientist who became known as "Dr. Germ" for helping Iraq make weapons out of anthrax.

Abu Ghraib is the prison where U.S. soldiers were photographed sexually humiliating male prisoners, raising fears about the safety about women detainees.

The speaker, whose voice resembled al-Zarqaqi, said Tawhid and Jihad was taking revenge for women Iraqi prisoners and called President Bush "a dog."

He said the next hostage would be killed in 24 hours unless "all Muslim women" are free from Iraqi jails. He did not specify which ones.

"You, sister, rejoice. God's soldiers are coming to get you out of your chains and restore your purity by returning you to your mother and father," he said.

In Georgia, Patty Hensley, the wife of Jack Hensely, pleaded Tuesday with his captors to open lines of communication and spare his life.

"I understand their political agenda, but what I need them to understand is the man who I have been with for 23 years, who is the father of our 13-year-old daughter, who does not understand this situation, why someone would want to hurt her father," Patty Hensley said in an interview with CNN. "I would plead with them to please realize this man does not deserve this fate."

In London, the Bigley's family appealed to British Prime Minister Tony Blair to meet the captors' demands.

"I ask Tony Blair personally to consider the amount of bloodshed already suffered," Craig Bigley, 33, said in a videotaped statement. "Please meet the demands and release my father — two women for two men. ... Only you can save him now. You have children and you will understand how I feel at this time."

Philip Bigley pleaded with his brother's captors to free his brother and Hensley.

"We are begging you not to kill them," he said. "We are begging you to find a solution, a compromise, that will help to save two lives, innocent lives."

Blair condemned the kidnappings at a news conference Monday.

"But our response has not got to be to weaken," he said. "Our response has got to be to stand firm, to say, whatever the differences over the Iraq conflict, there is a clear right and wrong on these issues, and that is to be with the democrats and against the terrorists."

In Washington, a U.S. official, speaking on condition of anonymity, said Armstrong's body had been recovered, but the official would provide no information about where or when it had been found.

The taped beheading appears to be of Armstrong, but the CIA is still reviewing the tape to be sure, the official said.

Armstrong grew up in Hillsdale, Mich., but left the area around 1990. His brother, Frank, still lives there. Armstrong's work in construction took him around the world; he lived in Thailand with his wife before going to Iraq.

"Jack (Eugene Armstrong) was a good guy," said Cyndi Armstrong, a spokeswoman for the Armstrong family. "He was in Hillsdale for many years, but he didn't like to stay in one place. He loved to travel."

Tawhid and Jihad — Arabic for "Monotheism and Holy War" — has claimed responsibility for the slaying of three hostages in the past, including the beheading of American Nicholas Berg, who was abducted in April. The group has also said it is behind a number of bombings and gun attacks.

More than 130 foreigners have been kidnapped in Iraq, and at least 26 of them have been executed. Iraqis have also faced an epidemic of kidnappings in the chaos since the fall of Saddam Hussein last year, in many cases for ransom.

In a separate hostage crisis, suspected Shiite fighters freed 18 U.S.-trained Iraqi National

Guards members Monday on the orders of renegade Shiite cleric Muqtada al-Sadr, who had denounced the act as insulting to Islam.

Insurgents have used kidnappings and bombings as their signature weapons in a 17-month campaign to undermined the interim government of Prime Minister Ayad Allawi and force the U.S. and its allies out of Iraq.

The violence continued unabated Tuesday with a police vehicle hitting a roadside bomb in Baqouba, north of Baghdad. One civilian was killed and four wounded, police and hospital officials said. Two policemen were also lightly injured.

On Monday, assailants gunned down two Sunni clerics in predominantly Shiite areas of Baghdad in twin attacks against a powerful Muslim religious group that has emerged as a key representative of Iraq's fearful Sunni minority. The Association of Muslim Scholars, a grouping of conservative clerics, opposes the U.S. presence in Iraq but has interceded often in the past to win the release of foreign hostages.