PESHAWAR, Pakistan — A suicide bomber killed 30 people attending prayers at a mosque, the latest violence to rock Pakistan's northwest just as the army says it is beating back the Taliban in the Swat Valley.

The attacks came as U.S. envoy Richard Holbrooke met with top Pakistani officials, including the prime minister, who requested the U.S. write off Pakistan's debt to help it tackle challenges including some 3 million Pakistanis made refugees by the Swat offensive.

Pakistani leaders insist they are serious about wiping out militancy in Swat, a one-time tourist haven that largely fell under Taliban control over the past two years. The U.S. backs the operation and sees it as a test of the government's resolve in taking on al-Qaida and Taliban militants along the Afghan border region.

The generally broad public support in Pakistan for the operation, however, could falter if militant violence spikes in reaction. There already have been attacks in major cities such as Peshawar and Lahore officials suspect were revenge by the militants for Swat.

There was no immediate claim of responsibility for the attack on the Sunni Muslim mosque in the Haya Gai area of Upper Dir, a rough and tumble district next to Swat. It was unclear if sectarian differences played a role, though the area is primarily Sunni.

"The latest report I just got is that 30 dead bodies have been identified. I cannot say how many more are dead, but there are scores of more wounded in the blast," Upper Dir district coordination officer Atif-ur-Rehman told The Associated Press by phone. He said a suicide bomber was involved and that rain and the far-flung nature of the area hampered rescue work.

Meanwhile, four soldiers were killed by a roadside bomb in South Waziristan, according to two intelligence officials who spoke on condition of anonymity because they were not authorized to speak to the media on the record. South Waziristan is a tribal region bordering Afghanistan that some suspect will be the next site of Pakistani military action against the Taliban.