ISLAMABAD, Pakistan - The favorite to be Pakistan's next president has moved into a guarded government compound over security fears, officials said Friday as a militant campaign against the government led to more violence in the country's volatile northwest.

The party of Asif Ali Zardari, the widower of the slain ex-Prime Minister Benazir Bhutto, has sought to assure the U.S. that it is committed to battling terrorists since Pervez Musharraf's resignation as president.

The country has been hit by a string of suicide bombings in the last two weeks, including one last week that left 67 dead, many of them civilians. More than 200 people have died in Taliban bombings and clashes since Musharraf quit on Aug. 18.

Prime Minister Yousaf Raza Gilani told reporters Friday that Zardari -- who is widely expected to win a Sept. 6 presidential election by lawmakers -- was staying at a hilltop mansion in Islamabad's government quarters "for security reasons."

He did not elaborate, but an intelligence official said there had been reports that the presidential hopeful could be the target of an attack and that he had switched locations after Musharraf's resignation.

The official spoke on condition of anonymity because of the sensitivity of the subject.

Pakistan's five-month-old government initially sought to calm militant violence by holding peace talks. But the initiatives have met with little success, and the government has since intensified military action against al Qaeda- and Taliban-linked militants in northwestern Pakistan. The tribal region along the Afghan border is a rumored hide-out of Osama bin Laden.

The militants, who have been pounded by helicopter gunships, have threatened more suicide bombings unless the operations cease. In the last week, they have hit one of the country's largest military installations, a hospital and a police station.

Troops foiled a suicide attack on a vital road tunnel in the region Friday, firing on a speeding vehicle that exploded and wounded 20 people, said Afzal Khan, a local police official.

Suspected militants also blew up two bridges in the area, said Kohat district administrator Mohammad Siraj Khan.

The U.S. worries that violence and political instability that followed Musharraf's resignation after nearly nine years in power will distract the nuclear-armed nation's efforts to fight extremists.

Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff, conducted a secret strategy session with Gen. Ashfaq Kayani, Pakistan's army chief, on an aircraft carrier in the Indian Ocean this week.