The most intense clashes seen in Damascus since the start of the Syrian uprising flared on Monday as loyalist units and guerilla forces battled near the city centre.
The ongoing fighting is believed to involve close to 1,000 opposition fighters and regime forces backed by armoured units, including tanks. Residents say fighting is centred in the suburbs of Midan and Zehera, not far from some of the capital's most secure areas.
There have also been clashes in the Tadamoun and Nahr Aisha neighbourhoods.
Witnesses say key sites, such as ministries and the presidential palace, remain far from the fighting. However, the road to the nearby Damascus international airport was closed for an hour on Monday morning, the first time that has happened since the initial anti-regime demonstrations in March last year.
Now, almost 17 months later, an armed opposition is continuing to show signs of being able to hold ground in strategically important areas, a far cry from even three months ago, when rebel groups were focusing on hit-and-run operations.
Damascus remains heavily defended by at least two loyalist divisions, which are not known to have suffered from defections among senior ranks. A wide variety of other loyalist forces and intelligence units have also been tasked with defending the power base of the regime.
Fighting started in Damascus on Sunday afternoon after opposition groups were seen advancing near Midan and staging for what appeared to be an assault. They were engaged by regime forces, which have so far been unable to rout them despite superior firepower.
The opposition assault appears to be a show of strength, more so than an attempt to take the capital – a task that still seems well beyond its capabilities.
However, the brazenness of the rebels, coupled with their newfound staying power, adds a fresh dimension to the uprising, which the International Committee for the Red Cross on Sunday cast as a civil war.
That designation acknowledges that two parties are now in full armed conflict and prescribes rules of warfare for each of them. Both regime and opposition forces are now obliged to protect civilian lives and areas, under threat of prosecution for war crimes if they fail to do so.
All of Syria's key cities have seen intensive clashes at times in the past year, during which nationwide demonstrations have steadily morphed into armed insurrection. The defiant street protests that defined the early days of the uprising still take place in many areas but are being dwarfed by an increasingly fractious series of clashes.
The already convoluted and fraught internal politics of the Syrian opposition is likely to take another dramatic turn in the next few days, when Manaf Tlass, a prominent Republican Guard general who defected to Paris earlier this month, is expected to a deliver a speech aimed at underlining his claims to a post-Assad leadership position.
"He is going to approach the political, military, and social vision for the future," said a close friend of the Tlass family.
"It will give his impression of all aspects – the FSA (Free Syrian Army), the regime, the regional situation, and the international setting. The speech is under construction and there are a lot of people working on it."
The family friend said that Tlass was consulting foreign governments as well as the opposition Syrian National Council about the speech. He added that in the 10 days since Tlass fled Syria the Assad regime has sent a series of intermediaries to try to lure him and his father, Mustafa Tlass, a former Syrian defence minister, back to Damascus.
"The regime sent messengers from every direction, offering the father a lot of sexy deals, that he was going to be vice-president and offering Manaf the ministry of defence," the friend said, adding that the Damascus government's recent public acknowledgement of Tlass's departure probably reflected its acceptance that he is not coming back.
"We expect that the moment Manaf goes public with his speech they are going to start attacking the family," the friend added.
Nawaf al-Fares, the former Syrian ambassador to Baghdad, also claimed that the Assad government, concerned that his defection was imminent, offered him promotion in an abortive bid to pre-empt his departure.
Fares told al-Jazeera over the weekend: "I was promised by Bashar al-Assad to be vice-head of the party. He told me this directly a short time ago, and his office talked to me a week before by my defection and told me to come back to Syria for this job … but what we have seen in the street, the suffering of the Syrian people, is bigger than any job."
The Tlass family friend also described the events that led General Manaf Tlass, formerly a close friend of the Assad dynasty, to decide to defect.
"After the crisis began Manaf was appointed to have a dialogue with nominated people in the uprising in Douma and Deraa," the friend said.
"But after these meetings Syrian security arrested those people who met him. He complained to Bashar al-Assad, asking why this is happening, and the president said: 'We are changing our strategy. We are not doing dialogue but we are cracking down.'"
"Manaf said he would not be part of this, and the president said: 'OK – you can go home and when we need you we will call you.' But they never did. So he sat at home, having lunch and dinner, going to his father's house, all under humongous surveillance."
Asked how Tlass managed to escape such close scrutiny, the friend said: "That is a complicated issue, which it would be better for him to explain in person."