By RIAZ KHAN

The Associated Press

DARGAI, Pakistan -- In the deadliest suicide attack on the Pakistani military, a man with explosives strapped to his body ran up to soldiers doing calisthenics Wednesday and blew himself up, killing at least 42 troops and wounding 20.

No one claimed responsibility for the attack, but suspicion fell on pro-Taliban militants who had vowed revenge for an airstrike that killed at least 80 people on a Muslim school the government said was being used to train militants.

The violence marked an escalation in the conflict between Pakistani security forces and Islamic militants along the rugged border, and sparked fears that the war in Afghanistan may be spilling into Pakistan, a key U.S. ally in the war on terror.

About 200 soldiers were exercising at an army training center in Dargai, a town 60 miles north of the capital of the North West Frontier Province, when the attacker struck.

"A man wrapped in a cloak came running into the training area and exploded himself where recruits had gathered for training," a military statement said.

Information Minister Mohammed Ali Durrani said 42 soldiers died and 20 were wounded. The army said some of the wounded were in critical condition.

Dargai is considered a stronghold of the outlawed Islamic group Tehrik-e-Nifaz-e-Shariat Mohammadi, whose fugitive leader, Faqir Mohammed, is a close associate of al-Qaida deputy chief Ayman al-Zawahri.

The Bush administration condemned the suicide attack and offered condolences to families and friends of the dead and wounded. "We applaud the government of Pakistan's determination and resolve to fight against terror," White House spokesman Gordon Johndroe said. "We stand with the government and people of Pakistan in this struggle."

Interior Minister Aftab Khan Sherpao linked the bombing to the Oct. 30 air raid on a school in the Bajur tribal region, which he said was targeted after officials received intelligence reports that "miscreants there were receiving training for suicide attacks."

Pakistan said it launched the airstrike with army helicopters, killing militants. But residents claim missiles were fired by American drones and that almost all the victims were children or teenagers.

The attack sparked furious protests across the country, and militants vowed to avenge the deaths.

President Gen. Pervez Musharraf's alliance with Washington in its war on terrorism has angered Islamic hard-liners, and the intrusion of Pakistan's army into semiautonomous tribal regions along the Afghan frontier has stoked unrest.

Over the past four years, the Pakistani military has waged a campaign in the border region, with limited success, to prevent the area from being used as a staging ground for militant raids on Afghanistan. About 80,000 Pakistani soldiers have been deployed to the tribal area, and hundreds have been killed in combat.

There has been a lull in fighting in recent months as the government sought a truce with tribesmen, but the Bush administration and NATO have exerted heavy pressure on Musharraf to rein in militants. The U.S. and NATO attributed the resurgence of the Taliban in Afghanistan this year and unexpectedly heavy allied combat losses to the guerrillas' use of Pakistan tribal areas as a sanctuary.

Hafiz Hussain Ahmed, a lawmaker from a hard-line Islamic coalition that is critical of Pakistan's military cooperation with the U.S., said he was saddened by the deaths in Dargai. But he criticized the government for fomenting the bloodshed.

"The government is to be blamed for today's attack. If you kill innocent students and teachers by attacking their school, you should be ready to face such things," he said. "People will not send you flowers if you kill children."

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AP writers Munir Ahmad and Slobodan Lekic in Islamabad contributed to this report.