SANAA - A Gulf-brokered deal to ease Yemeni President Ali Abdullah Saleh out of power teetered on the brink of collapse on Sunday after he refused to sign, raising the threat of increased instability in the Arabian Peninsula state.The pact would have made Saleh, a shrewd political survivor who has been in power for 33 years, the third ruler ousted by a wave of popular pro-democracy uprisings sweeping the Arab world. He had been due to sign the deal on Saturday.STILL HOPEFULBut Yemen's opposition said it still hoped Gulf states would extract Saleh's signature. Both Saleh and the opposition, which includes both Islamists and leftists, had agreed the deal in principle."The matter is now with the Gulf states. If they are able to persuade Saleh, that would be good," Mohammed Basindwa, an opposition figure tipped as a possible interim prime minister, said late on Saturday.A deal, if it is brought back on the table, would see Saleh appoint a prime minister from the opposition to head a transitional government, which would set a presidential vote for 60 days after he leaves. It would also grant immunity from prosecution to Saleh, his family and aides.Protesters say they will stay on the streets until Saleh leaves. They also called for him to be put on trial for corruption and the deaths of the estimated 144 protesters.In further violence, gunmen launched attacks with rocket-propelled grenades and gunfire on Sunday against a government building in the southern province of Abyan, killing three soldiers guarding the site and wounding four others, a local official said. He blamed the attack on al Qaida.Violence has also erupted recently in south Yemen, where analysts say the government, which has been trying to contain separatists in the south and Shi'ite rebels in the north, fears secessionists may be trying to take advantage of Yemen's leadership crisis to renew a push for separation.Analysts say a 30-day window for Saleh to resign would give plenty of time for disgruntled forces from the old guard to stir trouble in Yemen, where half the population owns a gun and al Qaida has gained a foothold in its mountainous regions.Yemen's opposition, furious over the last-minute change of heart, said it was considering escalating pressure on the president to step aside after three months of street protests demanding his ouster."We are studying the options of escalations and waiting for a U.S.-European stance on Saleh's refusal to sign," a senior opposition leader told Reuters, declining to be named because no formal decision had been taken.A Gulf source said a formal signing ceremony in Riyadh on Sunday in which the opposition had been due to seal the deal after Saleh signed in Sanaa was postponed. The source gave no word on whether or when it might be rescheduled.The United States and neighboring oil giant Saudi Arabia want the Yemen standoff resolved to avert chaos that could make a Yemen wing of al Qaida a greater threat to the region.Gulf Arab foreign ministers were to meet to discuss the crisis. But the opposition said it would not travel to Riyadh on Sunday to join the talks, saying there was no reason to attend.Gulf Cooperation Council mediators told Yemen's opposition on Saturday he would sign as leader of his party but had refused to sign in his capacity as president as required by the deal. The GCC secretary-general, who was in Sanaa for the signing, left Yemen without securing Saleh's signature.