ISLAMABAD – Pakistan’s main opposition party Sunday demanded the president give up the sweeping powers he inherited from his predecessor, setting the stage for political turmoil just as the Obama administration wants the country to focus on fighting the Taliban.

President Asif Ali Zardari’s grip on power is increasingly under threat from opposition lawmakers and elements within the powerful military who want him to resign or divest powers to the prime minister and take on a ceremonial role. Opinion polls show him to be desperately unpopular 15 months into a five-year term.

His presidency suffered another blow Saturday when an amnesty protecting him, several key allies and thousands of other officials from graft prosecution expired. While he enjoys immunity from prosecution as president, opponents could now go to the Supreme Court to challenge his eligibility for office.

Shahbaz Sharif, the brother of main opposition leader Nawaz Sharif and chief minister of Pakistan’s largest province, Punjab, said Zardari should act now to transfer the other powers to the prime minister, noting that the president had already promised to do so. “The nation would appreciate this act,” Sharif told reporters Sunday.

Late Sunday, Zardari said he would make an announcement “soon” on changes to the constitution needed to divest those powers, but the statement gave no specifics. He already promised at least twice to give up some of his authority to the prime minister since taking office.