Security forces killed as many as 70 militant fighters in Pakistan's volatile northwest on Thursday, an army spokesman said, hours after a homicide attack on an air force bus left eight people dead and dozens wounded.

Opposition leader Benazir Bhutto, seen by many supporters as key to a possible return to democratic rule, left the country to visit family in the United Arab Emirates, two weeks after she was targeted by assassins upon her return from eight years in exile.

Terror attacks and clashes between militants and President Gen. Pervez Musharraf's security forces have deepened the turmoil in Pakistan as it heads into elections and as the Supreme Court considers whether Musharraf can begin a new five-year term.

The violence in Swat, where a militant cleric is trying to enforce Taliban-style rule, is the clearest indication yet that the government is losing grip of large tracts of northwestern Pakistan, near the Afghan border.

Officials have now reported about 180 killed, mostly militants, in the past week since at least 2,500 security forces were deployed to tackle the followers of Maulana Fazlullah.

In the latest fighting, militants attacked law-enforcement posts before dawn, and security forces responded with fire from mortars, small arms and helicopter gunships.

"According to the information I have from police and Frontier Constabulary, between 60 to 70 miscreants were killed in Swat's areas of Khawaza Khela today," army spokesman Maj. Gen. Waheed Arshad said. Pakistan officials often refer to militants as "miscreants."

Sirajuddin, a spokesman for Fazlullah who goes by one name, denied the death toll, saying only one or two militants had died. He claimed that 40 security forces had surrendered in fighting in Khawaza Khela — denied by the provincial government.

"Security forces should join us and should not kill their Muslim brothers and sisters just for money at the behest of their non-Muslim masters," he told The Associated Press. "If they cannot join our ranks, we ask them to leave the (armed) services and go to their homes."

Sirajuddin also said militants had captured two foreigners in the area, but could not confirm local news reports that they were journalists or give their nationalities. He said the two would be investigated to establish their identities, then presented before the media.

Arshad said he had no confirmation that any foreigners were missing in the area.

Meanwhile, authorities were setting up a camp in Swat for some of the thousands of villagers displaced by the fighting, officials said.

In other violence, a suicide bomber on a motorbike rammed a Pakistan air force bus at around 7 a.m. near an air base in Sargodha, about 200 kilometers (125 miles) south of Islamabad, air force spokesman Sarfraz Ahmed said. All the dead were air force employees, said Sahid Malik, an official at the hospital treating the victims.

It was the latest in a series of attacks targeting security forces. There have been no claims of responsibility, but most of the bombings have been blamed on militants from the northwest.

Musharraf, a key U.S. ally, is under pressure from Washington to crack down on pro-Taliban and al-Qaida fighters hiding in those border regions near Afghanistan.

U.S. Central Command chief Adm. William Fallon arrived Thursday in Pakistan for a three-day official visit for talks with senior Pakistan military officials, state-run Associated Press of Pakistan news agency reported.

With his authority and political clout fading, Musharraf agreed to a corruption amnesty last month to help Bhutto return to Pakistan. That followed months of talks on a possible pro-Western alliance between them to counter Islamic extremism after parliamentary elections slated for January.

Bhutto's Oct. 18 homecoming was the target of the country's deadliest-ever suicide attack, claiming more than 140 lives.

She traveled to Dubai on Thursday and was expected to return home on Nov. 8 after visiting her children and ailing mother, said her spokesman, Farhatullah Babar. Earlier the former prime minister had said she intended to postpone the trip, citing lingering political uncertainties. It was unclear why she changed her mind.

The nation is awaiting a Supreme Court ruling on whether Musharraf's sweeping Oct. 6 election victory was unconstitutional, because he contested the vote while army chief. There are fears he could impose a state of emergency if judges rule against him, jeopardizing the country's transition to civilian rule.

Musharraf, who seized power in a 1999 coup, has pledged to quit the army before starting a new presidential term, but declined on election night to say whether he would accept a negative verdict from the court.

The Supreme Court, which in recent months has emerged as the main check on Musharraf's dominance, said Thursday that rumors of martial law would have no impact on its decision.

"No threat will have any effect on this bench, whether it is martial law or (state of) emergency," said judge Javed Iqbal before adjourning until Friday. The judge said the next session after that could be Nov. 12, three days before Musharraf's current term expires.

"Whatever will happen, it will be according to the constitution and rules," he said. "No group should think that it can take the Supreme Court hostage."