Pakistan is facing fresh political turmoil after party sources said the country's ruling coalition had agreed to impeach President Pervez Musharraf, a crucial US ally in the war on terrorism.

The agreement came after three days of talks between coalition leaders Asif Ali Zardari, the widower of murdered former prime minister Benazir Bhutto, and another former prime minister, Nawaz Sharif .

''The coalition parties have agreed in principle to launch an impeachment motion against President Musharraf,'' a senior coalition source said on condition of anonymity.

General Musharraf's spokesman was not available for comment but officials said he had again delayed his departure to Beijing, where he was to attend to the opening of the Olympic Games today.

Spokesmen for the two main parties in the coalition said a formal announcement was to be made last night.

General Musharraf seized power in a military coup in October 1999 and ruled nuclear-armed Pakistan for eight years with the backing of the United States, which has counted him as a key ally since the September 11 attacks.

But his popularity slumped after he ousted the country's chief justice and imposed a state of emergency in November 2007 to prevent challenges to his re-election as President.

General Musharraf stepped down as army chief that month, and the parties of Ms Bhutto and Mr Sharif then trounced his allies in general elections in February.

Coalition sources said the agreement to impeach came when Mr Sharif assured Mr Zardari on Wednesday that he could count on the support of some former members of the Pakistan Muslim League-Nawaz party who had joined a pro-Musharraf party.

A senior member of Mr Sharif's Pakistan Muslim League-Nawaz party said, ''There was a major breakthrough in the talks late last night. We have agreed to impeach the president.''

An official from Ms Bhutto's Pakistan People's Party, now led by Mr Zardari, confirmed the decision.

The parties have also agreed to restore judges sacked by General Musharraf under emergency rule but were still working out the details, the party sources said.

They said that a charge sheet on General Musharraf's position and performance as President would be drawn up and submitted to Parliament to be signed by at least half of all MPs in the coming days.

The speaker of the National Assembly, or lower house of Parliament, would then notify General Musharraf and ask him to defend his position within seven to 15 days, they said.

Television channels reported that the Government was set to recall the National Assembly as early as next week.

The Government is under huge US pressure over its efforts to negotiate with Taliban and al-Qaeda militants. It is also facing public anger over rising food and fuel prices. AFP