ISLAMABAD - A suicide bomber killed up to 10 people in Pakistan Friday, while a suspected U.S. drone killed six militants, as rising political tension threatened to distract the government from its war against the Taliban.

Opposition politicians have called for President Asif Ali Zardari to step down since the Supreme Court Wednesday threw out an amnesty that protected him, several government ministers and thousands of others from corruption charges.

The prospect of political turmoil would dismay the United States which has stepped up pressure on its nuclear-armed ally to tackle Afghan Taliban fighters in lawless border enclaves.

Pakistan has been battling homegrown Taliban who have responded with bomb attacks, but it is seen as reluctant to antagonize the Afghan militants who provide it with leverage against old rival India's growing influence in Afghanistan.

A suicide bomber struck near a mosque by a police compound in the district of Lower Dir.

We have 8 to 10 people killed. We have dead bodies as well as body parts and there are 28 wounded, said Jamal Hayat, a doctor at the region's main hospital.

At about the same time, a U.S. drone aircraft fired four missiles in the North Waziristan region, killing six militants, Pakistani security officials said.

Thursday, drones launched their heaviest ever strike in Pakistan, firing seven missiles at a militant cave complex, compound and vehicle, killing 12 fighters, officials said.

As the violence picks up, political problems mount for the unpopular Zardari, seen as close to the United States.

He has been dogged by accusations of graft from the 1990s when his late wife, Benazir Bhutto, served as prime minister.

He was included in the 2007 amnesty, which the Supreme Court threw out on the grounds it was unconstitutional.

Despite that, he cannot be prosecuted because he is protected by presidential immunity and his spokesman has said he will not quit. But several of his allies could face prosecution.

A spokesman for the state anti-graft agency said on Thursday the names of about 248 people had been placed on a list of people barred from leaving the country.

The spokesman did not identify any of those on the list but Defense Minister Chaudhry Ahmed Mukhtar, who had been included in the amnesty, was apparently one of them.

Mukhtar had been on his way to China Thursday when he was stopped at Islamabad airport. He was not available for comment but was reported to have dismissed the accusations against him.

The anti-graft agency issued a clarification later on Friday saying Mukhtar was not on the so-called exit control list. It did not say why he had been stopped at the airport.

But the bar on him leaving sparked rumors of a coup which swirled briefly in foreign exchange markets. The euro hit its lowest since March against the Swiss franc and the yen surged against the dollar. The currencies later recovered the worst of their losses.

STOCKS UNRUFFLED BY Rumor

The military, which has ruled Pakistan for more than half of its 62-year history, last staged a coup in 1999. Army chief General Ashfaq Kayani has vowed to stay out of politics but analysts say the army could intervene in the event of a crisis.

The president and army have had some differences but analysts scoffed at the possibility of a coup now.

Mutahir Ahmed, professor of international relations at the University of Karachi, said the army was fully engaged in fighting against the Taliban, while the people wanted to see the courts handle the corruption issue.

Stock investors did not take the rumor seriously although the main index ended 0.47 percent down at 9,183.73 as investors squared positions before the weekend, dealers said.

Interior Minister Rehman Malik was shielded by the amnesty as well and he and the defense minister also face calls to resign. Their departure from government would not have a big impact on the war against militancy, which is led by the army.

Some legal experts say the real danger for Zardari is that the legitimacy of his 2008 election as president could be challenged now that old cases against him have been revived.

The amnesty was introduced by former president Pervez Musharraf as part of a power-sharing deal brokered with Bhutto with U.S. and British encouragement.

Bhutto returned from self-imposed exile soon after the amnesty was introduced but was assassinated weeks later. Zardari led her party to victory in a February 2008 polls and became president after Musharraf stepped down.

His image, however, has long been tarnished by graft charges he says were politically motivated. He has never been convicted.

Pakistan's effort against the Afghan Taliban is critical to U.S. aims in Afghanistan. But ties have been strained by Pakistan's reluctance to heed U.S. pressure to crack down.

U.S. officials have warned Pakistan of more drone strikes if it does not go after the militants.

(Additional reporting by Faisal Aziz; Writing by Robert Birsel; Editing by Jerry Norton)

(For more Reuters coverage of Afghanistan and Pakistan, see: here)

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