Pakistani President Pervez Musharraf ordered a nationwide security crackdown Friday in an attempt to catch all suspects in the kidnapping and slaying of American journalist Daniel Pearl. 

"This incident has enhanced our resolve and in the days to come, I will deal with all kinds of terrorism with an iron hand," Musharraf vowed.

Dep. Secretary of State Richard Armitage spoke Friday morning with Pearl's widow, who is seven months pregnant, department spokesman Richard Boucher said.

"He expressed our condolences and our deepest sympathy for her loss. He expressed the sympathy and condolences both to her and to the child that they're expecting ... he stated very clearly to her...the commitment to bring to justice the people who are responsible for this horrible action," Boucher said.

Wall Street Journal reporter Pearl, 38, was confirmed dead by the U.S. State Department Thursday after the American consulate in Karachi received two videotapes depicting his murder, one longer than the other. 

Several sources told reporters that the videos showed Pearl's throat being cut. 

Four people have been arrested and charged in the case, including a British-born Islamic militant who admitted in court this week that he was behind kidnapping. A huge manhunt is underway for four other suspects, Interior Minister Moinuddin Haider told reporters.

Once they are apprehended, Haider said, "the whole net will be broken."

"We know their names and we know their identity," he added.

Pearl's body has not been found, and no details were immediately available on exactly where or when he was killed. 

The video confirming his death was obtained by a Pakistani journalist who gave it to the U.S. consulate on Thursday, a senior Pakistani official said. 

However, a source close to the investigation, who would not allow his name to be used, later denied that claim, saying someone posing as a journalist had obtained the tape. He would not elaborate further. 

President Bush reacted to the news in Beijing, where he was meeting with Chinese President Jiang Zemin, and said, "all Americans are sad and angry to learn of the murder."

Instructions have been given to all investigation teams to "apprehend the remaining culprits" as quickly as possible, said Mukhtar Ahmad Sheikh, interior minister of Sindh province, which includes the port city of Karachi. 

Those already arrested in the case include the alleged mastermind, British-born Ahmed Omar Saeed Sheikh, and three men accused of sending e-mails to news organizations announcing Pearl's kidnapping. 

On Thursday, one of the jailed suspects, Fahad Naseem, said before a Karachi magistrate that Saeed told him two days before the kidnapping that he was going to seize someone who is "anti-Islam and a Jew." 

Saeed, who was arrested last week, admitted his role in the kidnapping during a court appearance Feb. 14. Saeed told the judge he did not know Pearl's whereabouts but believed the journalist was dead. 

Since Saeed's arrest, the focus of the investigation has shifted to Amjad Faruqi, who is believed to have carried out the kidnapping. Police suspect that Faruqi — known to Pearl by the name Imtiaz Siddiqi — placed two calls to the journalist on the night he disappeared, apparently making Pearl think a meeting was being set up with a senior Islamic militant. 

A Karachi businessman involved in the investigation, Jamil Yousuf, said he met with Pearl shortly before he disappeared. Pearl received the two calls during a meeting at Yousuf's office, and the reporter told the businessman he was going to meet his contact at the Village Restaurant in Karachi. Restaurant employees told police they did not recall seeing Pearl that night. 

Faruqi is believed to be a member of Harkat ul-Mujahedeen, a banned Islamic extremist group with ties to Usama bin Laden's Al Qaeda network. Harkat ul-Mujahedeen is active in the struggle against Indian rule in disputed Kashmir, a Himalayan region claimed by both India and Pakistan. 

Last week, police raided Faruqi's home village in eastern Punjab province but found no trace of the suspect. They detained Faruqi's two brothers and three other villagers briefly. 

Police have mentioned the names of about 10 other suspects. They include Hashim Qadeer, whom Pearl knew as Arif. His family claims, however, that he was killed in Afghanistan. 

Complicating the probe, investigators say many of the suspects may be known by aliases. Police admit they are unsure whether one person may appear several times on the suspect list under different names. 

Investigators believe, however, that some of the kidnappers may have been involved in the December 1999 hijacking of an Indian Airlines jet to Kandahar, Afghanistan. During that incident, Indian authorities released Saeed and two other Islamic militants in exchange for the 155 passengers and crew. Saeed had been jailed in India in 1994 for kidnapping Western tourists. 

Pakistani analysts believe the kidnapping was staged to strike back at Musharraf for his support for the U.S.-led war on terrorism in Afghanistan and for his crackdown last month against Islamic extremists in Pakistan. 

I.H. Rashid, president of the Pakistan Federal Union of Journalists, which promotes press freedoms in the South Asian country, said his organization strongly condemns Pearl's murder. 

"The incident seems to be a fallout of the Afghan war," he said, adding that "there is anger and bitterness among followers of the extremist groups." 

Munawaar Hasan, a leader of Pakistan's right-wing Jamaat-e-Islami, or Islamic Party, said his group also condemns the killing because it violates the teachings of Islam, but he added that Muslims have good reasons to be angry. 

The Pearl case was "a reaction to the brutal state terrorism unleashed by America and its ally Israel on Muslims," he said. 

In a statement Friday, Pearl's widow, Mariane, who is seven months pregnant, said her husband's killers could not defeat his spirit and that she would tell their still unborn son that his father had worked to end terrorism.

Pearl's parents and two sisters said they were "shocked and saddened" by the news. 

In a statement, the Journal said Pearl's "murder is an act of barbarism that makes a mockery of everything Danny's kidnappers claimed to believe in. They claimed to be Pakistani nationalists, but their actions must surely bring shame to all true Pakistani patriots." 

Pearl was kidnapped in Karachi on Jan. 23 while researching links between Pakistani extremists and Richard C. Reid, the so-called "shoe bomber" arrested in December on a Paris-Miami flight he allegedly boarded with explosives in his sneakers. 

The kidnappers sent an e-mail Jan. 30 accusing Pearl of being a spy for the Israeli intelligence service, the Mossad. The Journal denied the allegation. 

The Associated Press contributed to this report.