The turmoil has left the party long led by slain former Prime Minister Benazir Bhutto in a position to dominate the government and it has been toughening its stance against Islamist extremists.
However, its one-time coalition partner on Thursday echoed widespread opposition to Pakistan's role in the U.S.-led war against terrorism.
U.S. officials have been pressing for more action against insurgent strongholds in Pakistan's wild border region, but Pakistan's military insists it is doing what it can to contain militants and prevent them from moving against NATO and Afghan troops on the other side of the border.
Pakistan's army chief secretly met the chairman of the U.S. Joint Chiefs of Staff, and other top American commanders Tuesday on an aircraft carrier in the Indian Ocean to talk about what else could be done.
The meeting aboard the USS Abraham Lincoln was the latest of several between Adm. Mike Mullen, chairman of the Joint Chiefs of Staff and General Ashfaq Kayani, chief of staff of the Pakistani army.
A U.S. official familiar with the discussion said Tuesday's meeting was "more collaborative," compared to a similar meeting a month ago when Mullen took a "more firm tone" in warning Kayani that Islamabad was not doing enough to counter militants waging cross-border attacks in Afghanistan.
However, a leader of the party that abandoned Pakistan's governing coalition called for a halt to Pakistan's weeks-old military offensive in the border region, saying the estimated 200,000 people who have fled the fighting to makeshift camps were suffering too much.
"Talking through the language of the bullet should be stopped," Chaudhry Nisar Ali Khan told reporters.
Thursday's powerful blast incinerated the car in which the bomb was hidden and left a massive crater in the middle of the long, concrete bridge near the city of Bannu.
The badly damaged bus smashed through a railing on the side of the bridge and tumbled about 30 feet into a mostly dry river bed below.
Jalil Khan, the local police chief, said the bus was en route to a local prison to pick up several inmates. He said seven policemen and an education department official who had hitched a ride were killed.
There was no immediate claim of responsibility, though police said militants were the likely culprits.
Musharraf resigned on Aug. 18, nine years after seizing power in a military coup, to avoid impeachment by political rivals who triumphed in February elections.
Former Prime Minister Nawaz Sharif pulled out of the coalition a week later over its failure to restore judges purged by Musharraf last year.
Lawyers who agitated for more than a year in favor of the judges and against Musharraf restarted their rallies Thursday.
Several thousand demonstrators blocked roads in a string of major cities. They also chanted slogans against Asif Ali Zardari, Bhutto's widower and the favorite to replace Musharraf when lawmakers select a new president on Sept. 6.
However, their numbers were smaller than in the past and Sharif's supporters largely stayed away.
