Witnesses described explosions and shooting in several areas just a few miles from the centre of the capital, but there was no sign that the army was losing control in what observers described as "serious but still localised" clashes.
Streets leading to Arnous and Saba Baharat squares, respectively a popular shopping area and the site of the Syrian Central Bank, were closed off, it was reported on social media sites. "Damascus is under heavy shooting, shelling by tanks and aircraft, siege," tweeted one activist from the suburbs of Damascus. Rebels also claimed to have shot down a helicopter over al-Qabun, scene of an attack on an electricity substation.
Sana, Syria's official news agency and the sole regular source of information from the government, said that security forces were "dealing with armed terrorist groups" in several areas of Damascus.
The rebel Free Syrian Army (FSA), the largest of the opposition armed groups, said it had launched "Operation Damascus Volcano" and called for an escalation of attacks on regime targets and the blocking of main roads around the country.
Colonel Qassim Saadeddine, the Homs-based spokesman for the FSA's joint command, said the fighting would not stop until the whole of the capital had been conquered, a Lebanese website said. "We have transferred the battle from Damascus province to the capital," he was quoted as saying. "We have a clear plan to control the whole of Damascus. We only have light weapons, but it's enough."
Damascus has seen fighting before, but usually at night. Three days of daytime combat seems to attest to the growing confidence of the rebels. Kefar Souseh, where shooting was reported, is home to many government offices. The city's international airport was apparently facing problems, with a report that a plane arriving from Kuwait was unable to land.
The tone of opposition statements did suggest a big development. "We are watching an epic battle for Damascus," commented the Syrian activist Amal Hanano on Twitter . "History is unfolding before our eyes. Long live the resilient Syrian people." But the latest fighting did not appear to have targeted any security installations, and observers expressed scepticism about claims of a large-scale rebel offensive. "It looks more like a publicity stunt designed to make an impact and encourage more defections," said the exiled activist Malik al-Abdeh. "The FSA can't sustain this sort of battle for very long."
In Paris, Manaf Tlass, a former Republican Guard general from a prominent Sunni family who defected on 6 July, issued a statement in which he called for "a constructive transition" and said the Syrian army had been made to conduct a fight against the Syrian people. "When I took a position and refused to take part in the security action, I was isolated, accused and even labelled a traitor," Tlass said in a statement to the French Press Agency. "But my conscience, my deep conviction, pushed me to challenge this destructive action and to distance myself."
Although the statement said he had no particular ambitions, a close friend of the Tlass family said it was intended to signal his willingness to play a leading political role in post-Assad Syria. The message was clearly intended to sound conciliatory, perhaps with the intention of positioning Tlass as a mediator in any transition.
"I sincerely hope that the blood stops flowing and that the country emerges from the crisis through a phase of constructive transition that guarantees Syria its unity, stability and security, as well as the aspirations of its people," the Tlass statement said. "I am ready like any other Syrian, with no other ambition, to fulfil my civic duty to contribute to a better future for my country, as much as I can, and like all those … who have already made many sacrifices."
In Israel, where officials watch Syria closely, the head of military intelligence, Major General Aviv Kochavi, told the Knesset foreign affairs and defence committee that Assad's fall was inevitable but estimated that it could take between two months and two years.
The Revolution Leadership Council in Damascus described helicopters and artillery firing on Barzeh. "The army is shelling al-Midan hysterically; the collapsing regime has gone mad," one local activist told AFP. None of the opposition claims could be independently verified due to restrictions on media access. The Local Co-ordination Committees activist group reported heavy shelling of rebel-held areas in the central province of Homs, where they said there were casualties.
The fighting continued as the Russian president, Vladimir Putin, met peace envoy Kofi Annan in Moscow. Speaking after the talks, Russia's foreign minister, Sergey Lavrov, said his country saw no reason why the UN security council could not find a consensus for a resolution on the Syrian crisis.
But Vitaly Churkin, Russia's UN envoy, insisted in New York later that the Kremlin would block a draft resolution on Syria if it is tabled . Russia has repeatedly said it would oppose any UN resolution that leaves room for foreign intervention in Syria and has opposed sanctions to Assad's regime.
British diplomats said there was no intention of threatening military action against Syria. Pressure was intended solely to force compliance with Annan's peace plan, which Moscow says it supports. "If the Russians choose to line up with the Assad regime, we'll have to see what comes next," said one official.
Jordan's foreign minister, Nasser Judeh, said that the kingdom has taken precautions to ward off a possible Syrian chemical attack – which he described as a matter of "grave concern".
William Hague, Britain's foreign secretary, who was visiting Syrian refugees in Jordan, warned that there can be "no impunity" for people committing human rights abuses in Syria.
The UN secretary general, Ban Ki-moon, called for rapid, unified action by the security council on Syria as he arrived in Beijing as part of a diplomatic push to get Russia and China to back a tougher response to attacks by Assad's regime.
There has been heightened urgency to global diplomatic efforts on Syria since it was reported last week that dozens of people were killed in a regime assault on the Syrian village of Tremseh. UN observers said the attack appeared to target army defectors and activists. Syria has denied UN claims that government forces used heavy weapons such as tanks, artillery and helicopters during the attack.
Iraq's government, meanwhile, called for all its citizens in Syria to return home immediately to escape the civil war after the recent killing of two Iraqi journalists.
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