"We tell the jealous people of mujahedeen of Pakistan," said al-Yazidd on the tape, which included English subtitles, "that in order for the jihad in Afghanistan to continue and be victorious, you must stand with your brothers the mujahedeen in Afghanistan to fight the puppet regime of Pakistan and its aggressive and tyrannical army and strike the interest of the Crusader allies in Pakistan."
Zardari, the new Pakistani president, delivered a nationally televised address after the bombing, promising to "rid Pakistan of this cancer. The day will come when all these people will bow in front of Pakistan's power."
Hours earlier, Zardari had spoken to a joint session of parliament, urging lawmakers to take a strong stand against the militants who operate from the Federally Administered Tribal Areas.
"I ask of the government that it should be firm in its resolve to not allow the use of its soil for carrying out terrorist activities against any foreign country," he said.
At least one member of the U.S. military was missing at the scene of the blast and presumed dead, according to a U.S. official in Washington. The official said other U.S. military members eating at one of the hotel's restaurants sustained non-life-threatening injuries. The U.S. embassy in Islamabad declined to comment.
The Federal Bureau of Investigation was monitoring the situation, spokesman Rich Kolko told ABC News.
"FBI teams are waiting to respond to the scene once several issues are coordinated by the State Department and U.S. ambassador in Pakistan," a bureau statement said.
The White House condemned the attack.
"The United States strongly condemns the terrorist attack that took place in Islamabad, Pakistan, today," said National Security Council spokesman Gordon Johndroe. "President Bush offers his sincere condolences to the families of all those lost in today's vicious attack. This is a reminder of the threat we all face. The United States will stand with Pakistan's democratically elected government as they confront this challenge."
Bush was briefed by National Security Advisor Stephen Hadley earlier today on the attack, Johndroe said.
More than two hours after the bomb, the hotel of 290 rooms was still on fire.
Mohammad Sultan, a hotel employee, told the Associated Press he was in the lobby when something exploded. He fell down and everything temporarily went dark. "I didn't understand what it was," he said, "but it was like the world is finished."
Brian Ross, Rehad El-Buri, Kirit Radia and Vija Udenans contributed reporting.