Youth and human rights activist leaders, who spearheaded Yemen’s populist rebellion, said Wednesday that they intended to launch their own transitional presidential council if the government refused to abandon President Ali Abdullah Saleh and pave the way for a transition of power.

The move underscored the sense of urgency and frustrations among the activists who fear, even with Saleh outside Yemen, they could lose the gains they have achieved so far and the regime could continue in Saleh’s absence.

“The only reason we are calling for the formation of a presidential council is because we feel the political powers have failed to take advantage of this historical moment when the president has left,” Tawakkol Karman, a prominent activist, told reporters, referring to Saleh’s loyalists.. “So we have taken the initiative.”

The drive to oust Saleh took on a new sense of urgency amid reports Tuesday that the injuries he sustained in an attack on his palace last week were more severe than previously stated.

In the streets of this tense capital, many youth activists see a greater opportunity to push through the democratic reforms they have fought for since launching a populist uprising in February. But Saleh’s supporters dismissed reports of his condition as exaggerated and appeared intent on demonstrating that without him, Yemen will remain engulfed in chaos.

U.S. officials said Tuesday that the 65-year-old autocrat suffered severe burn and shrapnel wounds that would prevent him from returning to Yemen anytime soon and raised doubts about his ability to rule.

“We have to take advantage of this moment,” said Riyad Zindani, 23, a student at Sanaa University. “A chance has been given to us on a plate of gold.”

If reports about Saleh’s condition are true, it could shift the balance of power in Yemen and speed up a political transition, diplomats and analysts said. Saleh’s extended absence would allow the United States and Saudi Arabia more time to persuade him to remain in exile. In Yemen, it could convince Saleh’s supporters — especially his sons and nephews, who continue to hold powerful positions in the security forces — that his nearly 33-year rule has come to an end.

That could pave the way for the acceptance of a power transfer initiative forged by the Saudi-led Gulf Cooperation Council, composed of Yemen’s neighbors — a proposal many here view as Yemen’s best hope for a peaceful transition of power. Even if Saleh were to return, though, his grip on Yemen would be severely weakened by his absence.

“When he is so badly hurt, and unable to function for at least several months, then it is inconceivable that he will be able to maintain power,” said Abdul-Ghani al-Iryani, a Yemeni political analyst. “And the main obstacle in the way of implementing the GCC initiative is now out.”

A U.S. official said that Saleh, who left Yemen on Saturday to seek medical care in Saudi Arabia, “sustained significant burn injuries and shrapnel wounds.”

“His condition is serious, and it’s likely that it will take him a while to recover fully,” the official said. Saleh has burns on about 40 percent of his body and suffered extensive injuries from wood splintered by the rocket attack on his palace, the official said.

But Saleh’s supporters on Tuesday dismissed the reports of his condition as overstated.

“The American government is mainly interested in a transfer of power from whomever to whomever,” said Ahmed al-Sufi, a presidential spokesman. “This is why they make up these stories. Definitely within a week, he will come back.”

A U.S. official, speaking on the condition of anonymity, said that Saleh’s son Ahmed, commander of the elite Republican Guard, had moved into his father’s office and that two of Saleh’s nephews are operating out of the palace.

The reports on Saleh’s condition arrived as attacks by militants and the Yemeni army in two restive provinces left dozens dead Tuesday. The ongoing bloodshed in Yemen underscores the potentially explosive political landscape in the strategic Middle Eastern nation, brought to the brink of civil war by two weeks of unrest and Saleh’s abrupt departure.

In southern Abyan province, a stronghold of al-Qaeda’s Yemeni branch, suspected Islamist militants attacked an army position late Monday, leaving nine soldiers dead, the Associated Press reported. Yemen’s Defense Ministry said the army killed 30 suspected al-Qaeda militants during the clashes, including a provincial leader.

Meanwhile, in the south-central city of Taiz, gunmen and soldiers fought late Monday and into Tuesday near the presidential palace. Four soldiers were killed, according to security and local sources. Republican Guard forces led by Ahmed Saleh shelled neighborhoods in the city early Tuesday, witnesses said. Two civilians were killed and 10 wounded, including women and children, medical officials said. Taiz has been a focal point of Yemen’s four-month populist uprising.

In the capital, a tenuous truce between government forces and opposition tribesmen brokered by Saudi Arabia on Friday continued to prevail. But a sense of trepidation and gloom spread across this sprawling city. Checkpoints manned by soldiers and police multiplied significantly. The road to a hotel frequented by Westerners was blocked by boulders and two sport-utility vehicles; police scrutinized passengers in every car.

In some neighborhoods, residents had left or were staying inside, creating a ghostly effect. An apparent fuel shortage underscored the dire economic conditions in a nation that is the poorest in the region. At gas stations, long lines of cars waited. Other Yemenis have turned to the black market, where the price of gas has more than tripled in recent weeks.

The violence appears to be an attempt by Saleh’s loyalists to maintain the balance of power in his absence. A cabinet meeting Tuesday focused on condemning the attack against Saleh, according to the official Saba news agency, and ministers unanimously vowed that it would not go unpunished. Meanwhile, state-run television has continued to broadcasts reports glorifying Saleh.

But if it becomes clearer that Saleh is not coming back soon, analysts said, the jockeying for power could be radically altered.

“Sooner or later, the people in Saleh’s camp will come to realize that Saleh’s regime has been decapitated and the best they could hope for is the smooth implementation of the GCC initiative,” Iryani said. “Any other option would be suicidal.”

Under the initiative, Vice President Abed Rabbo Mansour Hadi, who assumed control of the country in Saleh’s absence, would hand over power to a transitional presidential council that would run the country until elections are held.

Yemeni officials have debated whether to push through a transitional government or wait for Saleh to return from Saudi Arabia, even as they publicly contend that he remains firmly in control.

On Tuesday afternoon, thousands of youth activists began a 24-hour sit-in in front of Hadi’s residence. They demanded that he cede power to a transitional presidential council. Some called for a new constitution, with term limits for the presidency.

“We have to take advantage of [Saleh’s] departure,” said Yayha Hujeirah, 25, a law student. “We want the world to know Yemen can continue without him.”

Zindani worried that if a new political order is not created soon, Saleh will return and the chaos will grow. “It will be like a hurricane,” he said. “I don’t think Ali Abdullah Saleh will forgive what happened to him.”

Staff writers Greg Miller and Walter Pincus in Washington and a special correspondent in Sanaa contributed to this report.