By KAREEM FAHIM
SANA, Yemen — A day after President Ali Abdullah Saleh of Yemen handed over power to his deputy, effectively ending his 33 years of autocratic rule, his loyalists were accused of killing protesters on Thursday in an escalation of violence that raised questions about who is controlling the government’s militias.
At least five people were killed after gunmen in plain clothes opened fire on a rally intended to protest the power transfer agreement. It was the highest death toll in Sana, the capital, in weeks of protest marches.
Afterward, young activists posted what they said was a video of the attack, It showed a group of men, including at least one holding a picture of Mr. Saleh, firing machine guns and throwing rocks as protesters ran for cover.
Later, in a confusing twist, Mr. Saleh made a rare acknowledgment of the protesters’ claims, saying in a statement released through Yemen’s official Saba news agency that he condemned the violence. He also called for an investigation “to bring the perpetrators of this crime to justice.”
The killings — and Mr. Saleh’s public response to them — seemed to indicate that for the moment, Mr. Saleh intended to keep his hands in Yemen’s affairs. The developments occurred as the protesters, angered at the terms of the deal between Mr. Saleh and the mainstream opposition, fought among themselves and as opposition leaders jockeyed for positions in a new unity government.
Many of the protesters are particularly angry over clauses in the agreement that call on Yemeni lawmakers to grant Mr. Saleh and his aides immunity from prosecution. “Shame, shame,” they chanted.
The unrest caused one potential candidate for the new government to reconsider: Mohammed Basendwa, an opposition leader who had been rumored to be in the running for prime minister. “I don’t want it,” he said on Thursday. “This period is very critical and difficult. I might succeed. I might not.”
Violence elsewhere in the capital reinforced a feeling of unease. Mortar shells struck several buildings near the Parliament building, and clashes were reported in the northern part of the city between government troops and fighters loyal to a general who defected in the spring.
The agreement that Mr. Saleh signed on Wednesday raised hopes that his exit would end the 10-month political crisis, which began with street protests that called on him to leave power. The country had approached the brink of civil war as the government’s security forces killed protesters and fought with rivals of Mr. Saleh’s who command their own fighters.
By Thursday morning, it became clear that the circumstances of Mr. Saleh’s departure had aggravated rather than quieted the conflicts. At Change Square, a tent city in Sana that has become one of the focal points of the revolt, young activists fought with members of the Islamist opposition party, Islah, in a rare public show of discord.
“People think Islah sold out the revolution,” said Osamah Shamsan, one of the activists. “The square is in a mess. We all knew this was bound to happen.”
Within hours, dozens of the protesters who had marched from the square were brought back to a field hospital there in ambulances or on motorcycles.
Several of the wounded protesters said the gunmen were the plainclothes enforcers who have served as the government’s principal tool against the demonstrations.
“They were the thugs,” said Thiya Ayab, 21, who sat on a gurney with a bleeding wound in his thigh. “I just heard bullets.”
Nearby, photographers and onlookers crowded around the bodies of four young men, their names written on pieces of paper on their chests.
In his statement, Mr. Saleh said he would call on the interior minister to investigate the death of the “martyrs.” There were concerns, however, that Mr. Saleh’s statement was just more political maneuvering.
“With one order, he can stop these things,” said Abdul Rashid al-Faqih, a Yemeni human rights activist. “I think he’s trying to play two roles. He wants to satisfy the international community, but he didn’t take any steps on the ground to stop the mechanisms of attack on the protesters.”
“What happened today,” Mr. Faqih added, “is an indicator that he doesn’t want these things to stop.”
Protest leaders said large demonstrations were planned in cities throughout Yemen on Friday. They said that the marchers would continue to demand that any promises of immunity be revoked.
Opposition leaders like Mr. Basendwa, who argue that the agreement is necessary to move the country forward, have been forced to reckon with the anger that is mounting in the streets.
“They have every right to march,” he said. “Thousands of people have been killed. They have every right to be angry.”