Battle for Damascus begins as rebels strike near Assad's palace

Syrian rebel commanders claimed on Tuesday to have launched a military campaign to "liberate" Damascus as the city echoed to the sound of gunfire for a third day and fighting came close to the country's parliament building.

With an ever-bolder rebel assault threatening to expose Bashar al-Assad's increasingly tenuous hold on power, the Syrian president was accused of resorting for the first time to helicopter gunships to defend his once-impregnable capital.

Opposition fighters demonstrated their increasing confidence by launching hit-and-run attacks in the centre of the city close to some of the most heavily guarded symbols of government authority.

Firefights were reported within quarter of a mile of the Syrian parliament as well as outside the country's central bank. Shooting briefly forced the closure of Baghdad Street, one of the principal thoroughfares in central Damascus.

Other streets lay deserted as residents, once confident that they were far removed from Syria's turmoil, closed their shops and stayed at home. Hundreds of families were said to be fleeing the city.

Rebel commanders declared that the "Battle for Damascus" had begun, with fighters drafted into the city from other areas of the country as part of an operation they called "Damascus Volcano and Earthquakes of Syria".

"We have a clear plan to control the whole of Damascus," said Colonel Kassem Saadeddine, a spokesman for the joint command of the Free Syrian Army. "We only have light weapons, but it is enough." As in the previous two days, the bulk of the fighting took place in Sunni suburbs north and south of the city centre.

Rebel forces claimed to have shot down a government helicopter, though they provided no evidence. Video footage was released showing rebel fighters dancing around a captured armoured vehicle.

The FSA predicted that Assad's days were numbered. "We advise Bashar al-Assad to get out of Damascus now, otherwise he will die inside the capital," said Louay al-Mokdad, a logistical co-ordinator for the rebel group.

In what appeared to be a significant change of tactic by the armed opposition, he said that rebel units from Homs, Deraa and two other cities had been drafted into the capital. In a sign of Assad's desperation, government troops were recalled from other parts of the country to reinforce the capital. They included soldiers based on the border of the Israeli-occupied Golan Heights, Israel's head of army intelligence, Major Geneeral Aviv Kochavi, told a parliamentary committee in Jerusalem.

Tanks and lines of armoured personnel vehicles positioned themselves around the Midan, within three miles of the Presidential Palace. "The regime forces are using speakers telling people to leave. They are threatening to shell the area," said Tarek, a Damascus activist.

Gunfire rattled throughout the district as FSA rebels clashed with government troops and loyalist paramilitaries. Snipers were positioned behind sandbags on Midan's rooftops.

Although helicopters were seen flying above the city, it was unclear if there was any truth in rebel claims that they had opened fire on opposition strongholds.

Last night, General Manaf Tlass, a military defector, called for a political transition in Syria. In his first statement to the media since his defection was announced on July 6, General Tlass said the regime held "the majority of responsibility" for the crisis and confirmed he was in Paris.

A general in the elite Republican Guard charged with protecting the regime, General Tlass is the son of Mustafa Tlass, a former defence minister and close friend of Assad's late father and predecessor.

While the focus of Syria's civil war is shifting towards Damascus, it is far from certain that the rebels are yet in a strong enough position to take the capital.

Yesterday's clashes were more widespread than previous days, but they were also less intense, suggesting that some rebels may be on the defensive.

Despite suffering several military defeats in major cities, opposition fighters have clung on to their strongholds north of Damascus, particularly in areas close to the Turkish frontier. But their ability to hold territory closer to the capital has so far been much patchier.

Even so, Assad's position is weakening, a fact that appeared to prompt a small but potentially significant shift in Russian policy. Sergei Lavrov, the Russian foreign minister, declared that Moscow was ready to seek consensus in the United Nations Security Council over a resolution to end the Syrian conflict.

Meanwhile, gruesome video footage showing the corpse of the late Libyan leader Colonel Muammar Gaddafi being abused by the men who killed him was highlighted by Syrian activists as an example of what could happen to Assad. In the video, Gaddafi's body is seen lying in the laps of armed men in the back of a minivan. At one point, they use his head as a ventriloquist's dummy, though the sound quality is too indistinct to hear what they are making him "say".

A Syrian activist posted a link to the video on Twitter with the comment: "Someone needs to send this to Assad".

A crucial vote on Syria at the United Nations has been delayed as Western countries make a late effort to persuade Russia to threaten Bashar al-Assad with tough sanctions.

Western allies are determined to push ahead with a resolution, seen by The Daily Telegraph, that would trigger sanctions under Chapter VII of the UN Charter if the Syrian army does not withdraw its troops to barracks and stop using heavy weapons within 10 days.

The vote was due to be held today (Wednesday) at the UN's New York headquarters but has been put back to tomorrow evening or even Friday, when the two-month mandate of the UN observer mission in Syria expires.

Without a vote, the 30 observers would leave. Though its movements have been hampered, it has for two months provided the only independent reporting of the violence, which according to opposition estimates has so far claimed more than 17,000 lives.