Pakistani leaders failed Sunday to reach a deal on restoring judges sacked by President Pervez Musharraf, increasing the likelihood the ruling coalition could shatter after just six weeks in power and plunge the country back into political turmoil.

Negotiators from the two main ruling parties held talks in London throughout the weekend, ahead of a self-imposed Monday deadline to resolve the issue. But officials said Sunday night they were heading back to Pakistan without a deal.

Representatives of the junior party, that of ex-Prime Minister Nawaz Sharif, said members would meet Monday to consider whether to stay in the coalition. The party has already threatened to quit the Cabinet.

“We are still trying to take this matter to a satisfactory conclusion,” said Husain Haqqani, one of the negotiators for the larger party, that of Asif Ali Zardari, the widower of slain ex-Premier Benazir Bhutto.

Nawaz Sharif’s brother Shahbaz, who also was involved in the talks, said both sides had made sincere efforts to come to an agreement. He suggested an all-out opposition stand was unlikely.

“We will support the government issue to issue _ we will not let the government destablize,” he said. “I pray we could iron out these differences and give a good news to the nation tomorrow.”

Musharraf removed the judges and declared emergency rule in November to halt legal challenges to his presidency. Anti-Musharraf parties came to power after winning February elections, and promised to restore the judges.

But they have quibbled on the mechanics.

Sharif, who was tossed out by Musharraf in a 1999 coup, has pushed for the president’s ouster and demanded outright restoration of the deposed judges. A return of the judges could increase pressure on Musharraf, long a U.S. ally in the war on terror, to step down if the courts decide to revisit his eligibility for office.

But Zardari, who has been less harsh toward Musharraf, has linked the judges’ reinstatement to broader judicial reforms. Complex legal and political issues, including the status of the judges Musharraf installed after the purge, have proved stumbling blocks to a deal.

The two parties already missed an April 30 deadline to resolve the matter. Sharif later said the parties would introduce a parliamentary resolution to restore the jurists on May 12.

Information Minister Sherry Rehman, a key Zardari aide, said Sunday her party would try to work with Sharif’s even if the formal relationship breaks down.

“Our commitment is really to the people of Pakistan, not just to each other,” Rehman said. “If for some reason they decide to leave the coalition, we will try to continue to have a stable and good relationship.”

Sharif, however, sounded more downbeat.

“I think every Pakistani is disappointed with the outcome of these talks,” he said. “Despite very sincere efforts we have not been able to resolve the deadlock.”

Sharif and Zardari also met separately Sunday with U.S. Assistant Secretary of State Richard Boucher, who was visiting London. Elizabeth Colton, spokeswoman for the U.S. Embassy in Islamabad, confirmed the meetings.

She did not reveal what the meetings entailed but said reports that Boucher was there to “mediate” on the judges issue were unfounded.

“The restoration of judges is Pakistan’s issue to solve,” she said. “It is not for the United States to prescribe solutions.”

Of particular concern to negotiators is whether Musharraf and his allies could seek to block the return of Iftikhar Mohammed Chaudhry as chief justice.

Musharraf has accused Chaudhry of corruption and conspiring against his plan to guide Pakistan back to democracy after eight years of his military rule.

Zardari insists judges sworn into the Supreme Court after the purge be retained so they do not oppose the new government in a legal tussle that would cast the country into more turmoil.

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Associated Press writers Nahal Toosi and Sadaqat Jan contributed to this report.