Fighting continued for a fifth day near key government installations, indicating that Syrian President Bashar al-Assad's control is faltering. As the opposition advances, Russia and China still refuse to support a resolution calling for tougher sanctions. NBC's Ayman Mohyeldin reports.
Updated at 2:00 p.m. ET: As more Syrian rebels flooded into the country's capital, President Bashar Assad had reportedly left Damascus and was directing the response to the assassination of three top lieutenants on Thursday.
A day after a bombing killed his brother-in-law and two other key military figures, Assad was in the coastal city of Latakia, opposition sources and a Western diplomat told Reuters.
"Our information is that he is at his palace in Latakia and that he may have been there for days," said a senior opposition figure, who declined to be named, according to Reuters.
Latakia province is home to several towns inhabited by members of Assad's minority Alawite sect.
NBC's Ayman Mohyeldin reports on the escalating crisis in Syria, where President Bashar al-Assad is reportedly planning his response to Wednesday's bombing, which struck the heart of his regime.
On Thursday evening, Syrian television showed Assad swearing in Brig. Gen. Fahed Jassim el Friej as defense minister, the president's first public appearance since the stunning bomb attack on a crisis meeting of defense and security chiefs.
U.S. State Department officials said Thursday afterthey were not sure
A diplomat, who is following events in Syria, told Reuters: "Everyone is looking now at how well Assad can maintain the command structure. The killings yesterday were a huge blow, but not fatal."
NBC's Ayman Mohyeldin answers your questions about Syria
Ghazi Balkiz / NBC News
Ali Bakran is a commander of a Free Syrian Army brigade that operates out Jabal al-Zawiya.
Meanwhile, rebel fighters streamed into Damascus convinced that they could take over the capital and isolate the government.
"Taking Damascus will be a morale blow to Assad's regime," Ali Bakran, a commander of a Free Syrian Army brigade that operates out Jabal al-Zawiya, told NBC News.
Rebels from his region has sent about 1,000 fighters to Damascus over the last two days, he said.
Bakran said that once the rebels had taken control of the capital, they planned seize state radio and television stations -- a huge symbolic and tactical victory for anti-Assad forces.
PhotoBlog: Who are the Syrian rebels?
"Once we take over the TV and radio stations, the army will collapse," Bakran said.
'We will not stop'
And after Damascus, the rebels planned to march to Latakia, where Assad was reportedly staying, to "finish the job," Bakran added.
"We will continue our work, we will not stop, not after all this blood has been shed, not after all those innocents' deaths," he told NBC News.
Syrian rebels have kept up pressure following Wednesday's assassinations in Damascus, fighting loyalist troops within sight of the presidential palace and near government headquarters, residents said.
Residents said there was no let-up in the heaviest fighting -- now in its fifth day -- to hit the Syrian capital in a 16-month revolt against Assad, whose family has dominated the pivotal Arab country for 42 years.
The battles encroached within sight of the presidential palace, near the security headquarters where Wednesday's emergency meeting was held, with videos showing clouds of smoke rising over the skyline.
The defense minister, his deputy and a vice president were all killed in the blast but it is unclear if Syrian president Bashar al-Assad was nearby. NBC's Richard Engel reports.
The U.N. Security Council put off a scheduled vote on a Syria resolution until Thursday and President Barack Obama telephoned President Vladimir Putin of Russia, Assad's main ally, to try to persuade Moscow to drop support for him.
Nevertheless, Russia and China vetoed the resolution threatening sanctions against Syria.
The bombing that killed Assad's brother-in-law, defense minister and a top general triggered fierce army retaliation with artillery unleashed on rebels massed in several districts and armed mostly with small arms and rocket-propelled grenades.
A video from overnight in Damascus' neighborhood of Sayed Zainab shows a makeshift clinic in a house, with blankets and medical supplies strewn all over the floor and a man shouting directions on a megaphone as men carry in mutilated bodies on sheets.
Some of the bodies were blackened, perhaps from a blast or a fire. Others were blown apart apparently by high explosive.
Residents in the Midan and Kafr Souseh districts reported constant blasts and heavy gunfire as helicopter gunships buzzed overhead.
"The shelling did not stop all night. Shelling could be heard in all the city. It was loud. There were also sounds of clashes. Not many people are venturing out. I can't even find a taxi, so I'm waiting for somebody to pick us up," a resident in Damascus told Reuters, speaking by telephone.
PhotoBlog: Behind Syrian rebel lines
"Everyone in the neighborhood is arming themselves. Some with machineguns, some with shotguns. Some even just with knives. And whoever doesn't have anything just tries to stay awake and stay alert as much as they can," said another resident, speaking by phone from the Midan area.
For a third straight day, Syrian military fought rebels in the capital where activists say government tanks are fighting back. NBC's Ayman Mohyeldin reports.
"I can't even tell you what is going on outside because I've shuttered the windows and locked the doors. I just hear every now and then the gunfire, it's like it's in the room."
Many Damascenes were reported fleeing pockets of fighting.
"We've had a lot of people come in from last evening, from other neighborhoods like refugees, and people gather around them to hear what they've seen. My neighbor tries to see if they have relatives here or see if there is someone that can host them for a while," said a woman contacted by telephone.
Checkpoints around Midan and the ancient walled Old City of Damascus had been removed, residents said. It was unclear if security forces had changed tactics to stop rebels targeting soldiers, or if it was a temporary move in the heat of battle.
More world stories from NBC News:
Follow World News on NBCNews.com on Twitter and Facebook