The future of Pakistan's fledgling coalition government hung in the balance Monday after failed talks on how to restore judges sacked by President Pervez Musharraf.

The party of ex-Prime Minister Nawaz Sharif was set to discuss later in the day whether to abandon its alliance with the senior party of Asif Ali Zardari, the widower of slain former premier Benazir Bhutto. The relationship was forged after their victory over Musharraf's allies in February elections.

It remained unclear if the rift could break up the government or force fresh elections. That would be a serious setback to Pakistan's transition to democracy after eight years of military rule under Musharraf. The new government came to power just six weeks ago.

A coalition break-up could throw a political lifeline to the embattled president, who has taken a back seat in the day-to-day running of Pakistan since the new government took office.

Both parties still appear reluctant to sever ties. Although Sharif's party has threatened to quit the Cabinet _ a move that would distance it from the decisions of the government _ it has hinted it would still support the government rather than join the opposition.

Both sides have called for a restoration of dozens of judges axed by Musharraf when he declared a state of emergency in November to forestall a Supreme Court ruling on his eligibility for office. But they have disagreed on exactly how to do it and weekend negotiations in London did not produce a deal.

Sharif landed in Pakistan on Monday, the day he had set as a deadline for introducing a parliamentary resolution to restore the judges.

One sticking point appears to be over Iftikhar Mohammed Chaudhry, the independent-minded chief justice who emerged last year as a bulwark of opposition to Musharraf.

A return of Chaudhry and other judges would increase pressure on Musharraf, long a U.S. ally in the war on terror, and could set up a fresh confrontation with the president.

Sharif, whose last government was tossed out by Musharraf in a 1999 coup, has repeatedly called for Musharraf to resign, but Zardari appears more willing to work with him.

Zardari wants to link the judges' reinstatement to broader judicial reforms. Complex legal and political issues, including the status of the judges Musharraf installed after the purge, have also proved stumbling blocks to a deal.

The two parties already missed an April 30 deadline to resolve the issue of the judges. Sharif later said the parties would introduce a parliamentary resolution to restore the jurists on Monday.

Meanwhile, Sharif and Zardari met separately Sunday with U.S. Assistant Secretary of State Richard Boucher, who was visiting London, but U.S. officials denied the diplomat was attempting to mediate between the two leaders.

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Associated Press writers Nahal Toosi and Zarar Khan contributed to this report.