This hand out picture shows senior leaders of the Pakistan Muslim League-Nawaz submit presidential election nomination papers of retired Supreme Court judge Saeed uz Zaman Siddiqui (L) to Chief Election Commissioner Qazi Muhammad Farooq (R) at his office in Islamabad yesterday. Pakistani former premier Nawaz Sharif, who quit the ruling coalition on Monday over differences on the restoration of judges, has nominated Siddiqui to challenge co-chairman of Pakistan People's Party (PPP) Asif Ali Zardari for his party.Photo: AFP

Pakistan's political turmoil deepened yesterday after the two main parties in the ruling coalition split, weakening the fragile government just a week after president Pervez Musharraf resigned.
The world's only nuclear-armed Islamic nation, already facing a fresh campaign of bombings by a resurgent militant movement, now faces the prospect of a bitter political battle over the choice of Musharraf's successor.
Former prime minister Nawaz Sharif pulled his party out of the coalition on Monday, saying they were moving to the opposition because of what he said were the broken promises of the other main party's leader, Asif Ali Zardari.
He said Zardari had gone back on a pledge to reinstate dozens of judges sacked last year by Musharraf -- an issue that has been at the centre of a political dispute in Pakistan for the past year.
"We have taken this decision after we failed to find any ray of hope and none of the commitments made to us were fulfilled," Sharif said Monday. "This situation forced us to withdraw our support."
Zardari, in a televised address late Monday, appealed for Sharif's return to the government.
"We are sad over Nawaz Sharif's decision. We want to move together and solve the problems facing the nation," he said. "We will request Nawaz Sharif to return to the government."
Meanwhile, Pakistani stocks reacted negatively over the break up and slumped four percent on Tuesday. The benchmark Karachi Stock Exchange KSE-100 Index finished down 383.37 points to close at 9,430.29.
Lawyers meanwhile called for a nationwide protest on Thursday to demand the reinstatement of the judges, who were pushed out as Musharraf purged his opponents in the judiciary.
Sharif's PML-N party has put forward a candidate to challenge Zardari, widower of another former premier, Benazir Bhutto, on September 6, when lawmakers will select who will be the country's next president.
Zardari and the PML-N candidate, former judge Saeed uz Zaman Siddiqui, will face off against the party formerly behind Musharraf, which has nominated its secretary general, Mushahid Hussain.
Candidates filed their election papers on Tuesday.
Political chaos is nothing new in Pakistan, which has been under military rule -- including under General Musharraf -- for more than half of its existence since being partitioned from India after World War II.
But the months of turmoil that eventually forced Musharraf to resign last week under threat of impeachment, and the new split between Sharif and Zardari, have made Western allies jittery about Pakistan's role in the "war on terror."