Security and hospital officials say around 100 people have been injured after supporters of Yemen's embattled leader fired in the air to celebrate the reportedly successful surgery he underwent in Saudi Arabia.
The gunfire appeared to be a show of force by President Ali Abdullah Saleh's supporters.
The officials also say at least 40 private cars were damaged from the gunfire early Thursday.
The wounded included 20 people from a Sanaa square that has been the epicenter of protests demanding Saleh's ouster.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Saleh underwent surgery Monday to remove shards of wood from his chest and treat burns on his face and chest from an attack on his Sanaa compound.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
SANAA, Yemen (AP) -- Armed opposition tribesmen have seized control of part of Yemen's second-largest city, security officials said Wednesday, illustrating the breakdown of authority in the country amid a potentially explosive deadlock in the capital.
With the wounded President Ali Abdullah Saleh out of the country for treatment, the United States, Saudi Arabia and the Yemeni opposition are pressing for a formal end to his rule and the formation of a new government. But so far there's been little response from Saleh's ruling party, and his allies appear to be digging in, insisting the president will return soon.
That has left Sanaa locked in an uneasy cease-fire between government forces and opposition tribesmen barricaded in their positions after two weeks of heavy battles between them killed dozens. On Wednesday, tribesmen collected 10 more bodies of their fallen fighters from the streets of their main stronghold, Sanaa's Hassaba district, where most of the battles took place, a tribal spokesman said.
The United States fears that this power vacuum will give freer rein to al-Qaida's branch in Yemen -- one of the terror network's most active franchises, behind two attempted terror attacks on U.S. targets.
In a videotape released Wednesday, the deputy of slain al-Qaida leader Osama bin Laden sought to adopt the anti-Saleh movement. "We are with you in your uprising," Ayman al-Zawahri said in the video posted on Islamic militant websites. He warned Yemenis not to be tricked by the Americans and their Gulf allies "who want to replace one American agent with another," urging the opposition to continue until Saleh's regime falls and "they put in its place a just regime that rules by Islamic law."
On a visit to Egypt on Wednesday, Chairman of the U.S. Joint Chiefs of Staff Adm. Mike Mullen said Washington was particularly concerned about al-Qaida's branch gaining a greater range of operations.
"It is incredibly dangerous and made that much more dangerous in the ongoing chaos," Mullen said. "I would certainly urge leaders from every side of this challenge to be calm and try to resolve the issues peacefully."
Hundreds of thousands of Yemenis, inspired by uprisings elsewhere in the Mideast, have been protesting daily since late January demanding the ouster of Saleh, who has ruled Yemen for nearly 33 years. Their campaign has been largely peaceful, but fighting erupted in Sanaa between Saleh loyalists and fighters from Yemen's most powerful tribal confederation, the Hashid, after troops moved to attack the residence of the Hashid leader, Sheik Sadeq al-Ahmar.
The fighting continued until Friday, when a rocket hit Saleh's presidential palace, killing 11 of his guards and wounding the president. Saleh, in his late 60s, was taken to Saudi Arabia with severe burns -- U.S. officials say they cover 40 percent of his body -- and chunks of wood in his chest.
While the cease-fire has largely held in Sanaa, fighting has raged the past two days in Taiz, Yemen's second largest city. Taiz has been the site of major protests, and last week government troops cracked down hard, breaking up the protesters' camp in a main square and killing more than 20.
In recent days, tribesmen from the Taiz region sympathetic to the protesters rose up and attacked government forces, with two days of clashes around the local presidential palace this week. Amid fighting Tuesday, a tank near the palace fired a shell into a residential neighborhood, killing four people, including three children. Houses around "Freedom Square," the public square where the protests were centered were severely damaged, witnesses said.
On Wednesday, security officials said tribesmen were now in control of large parts of the city of around 1 million, located 150 miles (250 kilometers) south of Sanaa. The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Sheik Hamoud Said al-Makhlafi, a tribal chief in the region, said local tribes had moved to protect protesters, though he denied tribesmen controlled the entire city. Witnesses said protester "citizen committees" were now controlling neighborhoods and some government buildings, while government forces remained centered around the palace and a main hospital.
Army units backed by tanks that were moving to reinforce government troops in Taiz were attacked by opposition supporters in the nearby city of Qaida, witnesses said. After an hour-long battle, the force was able to push through toward Taiz, they said.
The fighting in Taiz underlined that the deadlock in the capital is unlikely to remain relatively peaceful for long, with Saleh's opponents pressing for a definitive end to his rule. Currently, Vice President Abed Rabbo Mansour Hadi is acting president, but Saleh did not formally hand over power and his officials claim he will return within days.
The United States and Saudi Arabia are pressing for the revival of an accord by which the vice president would formally take power, a unity government would be formed with the ruling and opposition parties and elections would be held within two months.
But the opposition has its own divisions. Official opposition parties say they accept the deal. But the youth groups behind the massive anti-Saleh street protests reject it, saying it would only keep vestiges of Saleh's regime in place.
On Wednesday, a key coalition of the anti-Saleh youth groups called for an immediate start to consultations with political groups to set up an interim council along with a government of technocrats to run the country until elections were held and a new constitution was drafted, spokeswoman Tawakul Karaman told a news conference.
Karaman warned Hadi that he has the choice of either supporting the "revolution" or be held to account as a member of the Saleh regime.