Clashes between Yemeni forces and anti-government protesters have left at least six people dead amid a political power vacuum after President Ali Abdullah Saleh left the country for treatment of wounds suffered in a rocket attack.
Saleh's advisers said he expects to return to Yemen, though others see his departure as a de facto resignation.
The latest violence threatened a cease-fire brokered by Saudi Arabia's King Abdullah on Saturday as Saleh flew to the Saudi capital of Riyadh for surgery.
The office of Yemeni opposition tribal leader Sheik Sadeq al-Ahmar said three of his supporters were shot dead in the tense Hassaba neighborhood in the north of the capital, Sanaa. A defecting military official said three other people were shot to death late Sunday when government gunmen opened fire on their checkpoint.
The clashes also risked undermining the position of Vice President Abdel Rabo Mansour Hadi, who has assumed authority in Saleh's absence. Deputy Information Minister Abdu al-Janadi has insisted the president's absence is only temporary, despite months of often violent protests aimed at ending his more than three decades in power.
Opposition figures have said a swift transition to a post-Saleh era is essential, but analysts have warned that it might not be easy. It would require Saleh's willingness to formally relinquish power and call for delicate negotiations among Yemen's fractious and well-armed tribal and regional factions.
Political analyst Abdul Ghani al-Eryani, speaking to NPR from Sanaa, said Saleh was already working out the details of a power transfer when he was wounded, making his return doubtful — especially amid such intense domestic opposition and international pressure for his resignation.
"The day he was attacked, he was meeting with his top lieutenants to agree on signing a peaceful transfer of power deal," al-Eryani said.
But an opposition party official told The Associated Press on Sunday that international mediators, including the U.S. and Saudi Arabia, tried to get Saleh to sign a presidential decree passing permanent authority to his vice president before he left for treatment in Saudi Arabia.
Saleh refused to sign the deal sponsored by the Gulf Cooperation Council — following a pattern established over the past few weeks after he initially agreed to sign it — and offered only a verbal agreement, but the negotiations delayed his departure, the official said.
The apparent pressure from Riyadh, which has long backed Saleh, reflects Saudi concerns that unrest in Yemen could spill over their mutual border. Saudi Arabia also is monitoring a similar uprising in neighboring Bahrain.
Saleh underwent successful surgery on his chest to remove jagged pieces of wood that splintered from a mosque pulpit when his compound was hit by rockets on Friday. Officially, he was expected to remain in the kingdom for two weeks: one for treatment and another for meetings with Saudi officials.
The rocket strike, which the government first blamed on tribal fighters and later on al-Qaida, killed 11 bodyguards and seriously wounded five senior officials worshipping at Saleh's side.
On Monday, jubilant protesters continued to take to the streets of Sanaa to celebrate Saleh's departure. In contrast to other reports of violence, political analyst al-Eryani said he witnessed only peaceful demonstrations.
"The celebrations are still going on. There is quiet in the city; there is no violence," he said.
Still, many Yemenis fear that Saleh will either return or leave the country in ruins if he cannot retain power.
His absence also raises the specter of an even more violent power struggle between the armed tribesmen who have joined the opposition and loyalist military forces under the command of Saleh's sons and nephews. The two sides have been locked in a standoff in the two weeks since the president's forces attacked the home of a key tribal leader and one-time ally who threw his support behind the uprising, turning the streets of Sanaa into a war zone.
Al-Eryani told NPR that he thought all-out civil war could be averted if Saleh cedes power permanently.
"I think the departure of the president reduced the risk of civil war," he said. "I think the tension is still there, but it will dissipate as soon as a political agreement is reached."
Yemen's rebellion began as a peaceful protest movement that the government has, at times, used sheer force to suppress. At least 166 people have died since the unrest began, according to Human Rights Watch.
In Taiz, Yemen's second-largest city, dozens of gunmen attacked the presidential palace on Sunday, killing four soldiers in an attempt to storm the compound, according to military officials and witnesses. They said one of the attackers was also killed in the violence. The attackers belong to a group set up recently to avenge the killing of anti-regime protesters at the hands of Saleh's security forces.
Elsewhere in the south, gunman ambushed a military convoy, killing nine soldiers, officials told the AP. They spoke on condition of anonymity because they were not authorized to talk to the media.
NPR's Peter Kenyon reported from Cairo, Egypt, for this story, which contains material from The Associated Press.