Pakistan's Supreme Court said Tuesday it will soon begin examining a recently expired graft amnesty covering the president and key allies. The decision launches a process that could eventually unseat the U.S-allied leader just as the Obama administration needs stability in Islamabad to help crack down on the Taliban.

Highlighting the dangers, a suicide bomber killed an anti-Taliban lawmaker in the northwestern Swat Valley — the latest in a series of bombings as the army presses offensives into militant strongholds close to the Afghan border.

President Asif Ali Zardari, who is languishing in public opinion polls, has been under mounting pressure to resign or relinquish key powers to the prime minister and assume a ceremonial role.

Those calls came to the fore with Saturday's expiration of an amnesty that had been granted to him and more than 8,000 other politicians and bureaucrats under his predecessor.

A statement issued Tuesday said the Supreme Court has received petitions calling the amnesty a violation of fundamental rights. It said the court has notified all concerned parties that it will start proceedings into the cases on Monday.

The amnesty was part of a deal with Musharraf that paved the way for former Prime Minister Benazir Bhutto to return home from self-exile and take part in politics without facing cases her party says were politically motivated. Zardari took control of the party after Bhutto died in a suicide bombing on Dec. 27, 2007.

But the amnesty expired on Saturday, opening the possibility that opponents could petition the court to challenge his eligibility for office. Zardari generally enjoys immunity from prosecution but legal experts have said that could be revoked if the amnesty were determined to be illegal.

His office declined to comment on the Supreme Court's decision.

While the legal process is likely to take months and is far from certain to deliver a fatal blow to Zardari's presidency, the speed with which the court announced its intention to hear the petitions suggests it wants to move ahead forcefully with the case.

Earlier this year, Zardari gave in to street protests and reinstated Iftikhar Mohammed Chaudhry as the chief justice after he was fired by Musharraf. Many analysts took Zardari's reluctance to restore Chaudhry as a sign he feared Chaudhry would try to undermine his rule from the bench.

Zardari, 54, has long been haunted by corruption allegations dating back to governments led by his late wife, Bhutto, and has spent several years in prison under previous administrations. He denies any wrongdoing.

The opposition also has called on Zardari to give up sweeping powers he inherited from Musharraf.

Pakistan's original constitution envisaged a parliamentary style of government, in which a popularly elected prime minister is the chief executive and the president is a ceremonial head of state. But Musharraf, who was widely despised when he stood down, accumulated powers to stay in office.

Zardari relinquished command of the country's nuclear arsenal on Friday and has said he would give up more powers in the near future.

The domestic woes have threatened to distract the administration as it battles Taliban and al-Qaida militants on the border.

President Barack Obama telephoned Zardari on Tuesday night to outline his new Afghan strategy.

"President Barack Obama mentioned the broad outlines of the U.S. Afghan policy," Zardari's office said in a statement. "President Obama reaffirmed U.S. commitment to a long-term partnership with Pakistan for security and stability."

Washington's strategy — expected to be announced by Obama later Tuesday — envisages an expanded partnership with Pakistan in return for increased efforts to root out extremists in the border area while the U.S. sends thousands more troops to Afghanistan.

Islamabad, however, has expressed fears that a surge in American troops could drive more extremists across the border.

The suicide bomber blew himself up among guests greeting provincial assembly member Shamsher Khan in his house close to the main Swat Valley town of Mingora, police and hospital officials said. Nine other people were wounded, including the lawmaker's brother.

Khan, 59, was a member of the secular Awami National Party and a vocal supporter of army offensives against militants in the region, as well as education for girls.

Regional police chief Idrees Khan said the bomber's head was severed from his body and he appeared to be about 16 years old.

Swat Valley was the site of a military offensive this summer that was largely considered a major success. But sporadic bombings and clashes still occur, raising fears many of the militants escaped and could regroup.

Similar concerns have been expressed about a major army assault that began in mid-October in the border region of South Waziristan that has reclaimed several towns.