President Pervez Musharraf said in an interview published Friday that U.S. troops would be regarded as invaders if they crossed into Pakistan to hunt Al Qaeda militants.

He also said he would resign if opposition parties tried to impeach him after next month's elections.

Musharraf's remarks in an interview with Singapore's The Straits Times came as police tried to identify a suicide bomber who struck a day earlier in Lahore, killing 24 people and adding to pressure on the former general as he struggles to stay in office eight years after seizing power in military coup.

Pakistan is under growing U.S. pressure to crack down on militants in its tribal regions close to the Afghan border.

The rugged area has long been considered a likely hiding place for Al Qaeda leader Usama bin Laden and his top deputy, Ayman al-Zawahri, as well as an operating ground for Taliban militants planning attacks on coalition forces in Afghanistan.

The New York Times reported last week that Washington was considering expanding the authority of the CIA and the U.S. military to launch aggressive covert operations within the tribal regions. Several U.S. presidential candidates have also hinted they would support unilateral action in the area.

Musharraf told The Straits Times U.S. troops would "certainly" be considered invaders if they set foot in the tribal regions.

"If they come without our permission, that's against the sovereignty of Pakistan. I challenge anybody coming into our mountains. They would regret that day," he said in the interview.

Musharraf is also under gathering domestic political pressure. The party of slain opposition leader Benazir Bhutto and the other main opposition grouping are predicted to make gains in the Feb. 18 election. They have vowed to oust Musharraf if they emerge as winners. Musharraf is seen as vulnerable to impeachment over his decision last year to fire Supreme Court judges and suspend the constitution.

"If that (impeachment) happens, let me assure that I'd be leaving office before they would do anything. If they won with this kind of majority and they formed a government that had the intention of doing this, I wouldn't like to stick around," he said. "I would like to quit the scene."

Thursday's blast targeting police officers outside the High Court in the eastern city of Lahore was the latest in a series of bloody attacks.

At least 20 suicide bombers have struck in the past three months, killing 400 people, many of them from the security forces — the most intense period of terrorist strikes here since Pakistan allied with the U.S. in its war against Al Qaeda and other extremist groups in 2001.

Lahore police chief investigator Tasaddaq Hussain said the mutilated head of the suicide bomber had been recovered and would be reconstructed for identification. The bomber's other remains were being examined by forensic experts to extract DNA, he said.

"This is an act of terrorism and militants are to be blamed for it," Hussain said.

Later, about 200 lawyers prayed for the victims outside the court and laid flowers at the scene.

Police said the attacker was amid some 70 officers in riot gear when he detonated explosives on his body. All but three of the dead were police.

There was no claim of responsibility. The government has blamed previous attacks on Islamic radicals allied with Al Qaeda and the Taliban sheltering in the tribal regions along the Afghan border.

Musharraf blamed the same militants for the Dec. 27 gun-and-suicide-bomb attack that killed Bhutto, a secular former prime minister who had repeatedly pledged to battle Islamic extremism in this country of 160 million people.

Bhutto's supporters have questioned whether elements within the government may have had a role in her slaying and are demanding an independent U.N. investigation. To allay critics, Musharraf last week invited British police to help investigate.