— Yemenis set off fireworks and danced in the streets on Sunday to celebrate the possible end of President Ali Abdullah Saleh’s reign, as opposition politicians and diplomats scrambled to hatch a plan to stop an ongoing, violent power struggle.

The jubilation that gripped Sanaa, the capital, was tempered by fresh clashes in the southern city of Taiz, as well as myriad unanswered questions about how, and whether, a change of guard would play out. Residents in Sanaa reported loud explosions and sustained gunfire Sunday night, but few details about the violence were available.

Saleh temporarily ceded power to his vice president Saturday night to travel to Saudi Arabia for surgery, a day after having been wounded in a rocket strike on his palace.

Saleh, a key U.S. ally in the fight against al-Qaeda, has struggled in recent months to weather a youth-led uprising, launching brutal crackdowns that left scores dead and prompted Western allies and powerful tribes to turn against him.

In meetings Sunday, American and European diplomats, including U.S. Ambassador Gerald M. Feierstein, urged opposition politicians to refrain from setting up interim government committees before Saleh is formally out of power, fearing that such a move could unleash a violent response, an opposition leader said. He spoke on the condition of anonymity to discuss private meetings.

Saleh’s sudden departure renewed hopes among diplomats and opposition leaders that the 65-year-old autocrat could be persuaded to relinquish power under the terms of an agreement proposed last month by Saudi Arabia and other Persian Gulf states.

Ruling party senior officials and the Joint Meeting Parties, which make up the opposition, have signed the agreement. Saleh, however, backed out at the last minute on the deal, which would have granted him immunity from prosecution as long as he stepped down promptly.

“The ball is now in their court,” said Mohammed Qahtan, a spokesman for the opposition coalition, referring to the president and male relatives who command elite military forces. “The question is whether they will accept the transfer of power in line with the constitution,” and the Gulf States-brokered deal.

A U.S. embassy spokeswoman said Sunday that she could not discuss the substance of Feierstein’s meetings but made clear that the United States continues to attempt to push its onetime ally out of power.

“The ambassador is continuing to meet with all sides to try to come up with a process for a peaceful transition,” the spokeswoman said Sunday.

Yemeni officials, meanwhile, sought to portray the president’s trip as a short absence. The state-run news agency issued a statement Sunday noting that Saleh’s relatives did not accompany him to the neighboring kingdom — an apparent effort to signal that the Saleh era has not yet come to an end.

Saleh's’ relatives have played a key role in the recent clashes with the powerful tribal militias led by Sadeq al-Ahmar, which turned on the government after security forces used lethal force against unarmed protesters last month.

Saleh blamed the Ahmars for the attack on his palace and appears to have directed government forces to respond by launching a days-long artillery assault on their homes in Sanaa.

“The animosity between the Ahmars and the Salehs has been getting worse over the last decade,” Sarah Phillips, a Yemen expert at the University of Sydney, said Sunday. “I would imagine [Saleh’s] nephews and sons will be wanting revenge.”

Another key unanswered question was how Saudi Arabia would use its expanded leverage — now that Saleh is in the neighboring kingdom — to attempt to push through a transition deal.

“The Saudis have pursued a policy that kept Yemen weak enough that it didn’t challenge Saudi,” but strong enough so it wouldn’t pose a threat, said Gregory Johnsen, a Yemen expert at Princeton University.

The kingdom appears to have turned its back on Saleh in recent months as it became increasingly clear that his refusal to resign threatened to plunge Yemen, already a hub for Islamic terrorists, into lawlessness.

“Instability tends to slip over,” said Kenneth Katzman, a Middle East expert at the Congressional Research Center, the U.S. Congress’s think tank. “First and foremost, the Saudis want stability.”

The prospect of a democratic Yemen, however, is likely to make Saudi officials uncomfortable because democratic reforms could put pressure on Gulf states to take similar steps, analysts said. “They don’t want to see a systemic change in Yemen,” Phillips said.

Even as fighting in the capital and the south continued, many saw Sunday as the end of Saleh’s 33-year rule.

“The nightmare is gone,” cried out Fatima Ahmed, 72, as she clutched an umbrella to shield her skin form the sun. “The Yemeni people have been born again.”

A Washington Post special correspondent in Sanaa contributed to this report.