Zardari, the widower and political successor of slain ex-Prime Minister Benazir Bhutto, was one of those who benefited from the reconciliation ordinance, analysts said.

While the PPP feared that the provisional constitutional order and the reconciliation ordinance would become invalid if the sacked judges were reinstated, losing their immunity, the PML-N insisted on firing the current judges appointed after Nov. 3 and said it would join protesting lawyers to demand a quick reinstatement of the fired judges.

Latent crisis

The PPP has been preparing itself for a situation once the PML-N withdraws from the ruling coalition, analysts said.

Zardari did not say whether the ministers' resignations would be accepted or not. But with a majority in parliament even without Sharif's party, he could bring other parties into his government, analysts said.

The Muttahida Qaumi Movement said on Monday that if the PML-N decided to pull out of the coalition government, the movement was ready to join the coalition at any time.

Room for negotiations

Despite their differences, both the PPP and the PML-N agreed to maintain the integrity of the ruling coalition, which they believed was conducive to Pakistan's stability and democracy process.

Sharif said on Monday that his party withdrew from the cabinet, not the ruling coalition.

"The PML-N will not join the opposition for now," he added.

Prime Minister Yousaf Raza Gilani also called for a last-ditch effort to save his government Tuesday, after refusing to accept the resignations.

There was room for further negotiations as the two political parties have expressed willingness to continue cooperation.