Heavy explosions shook the Syrian capital today and helicopters circled overhead as rebels appeared to be renewing their offensive in the city, witnesses and activists said.

The fresh battles in Damascus show that President Bashar Assad's victories could be fleeting as armed opposition groups regroup and resurge, possibly forcing the regime to shuffle military units to react to attacks across the country.

The country's civil war has intensified in recent weeks as rebels focused on the country's two biggest cities, Damascus and Aleppo.

"We heard heavy bombing since dawn," a witness in Damascus told The Associated Press. "Helicopters are in the sky."

Today's violence comes only two weeks after the government crushed a rebel run on Damascus which included incursions by fighters into central areas and an audacious bomb attack which killed four members of Mr Assad's inner circle.

The fighting in Damascus appeared likely to drain the army's resources as fighting stretches into its second week in Aleppo, 215 miles (350km) to the north.

Late yesterday , Syria's official news agency Sana said government forces had hunted down the remnants of the "terrorist mercenaries" - its term for the rebels - in the capital's southern neighbourhood of Tadamon. It said several were killed and many others wounded.

Syria's uprising began in March 2011 with mostly peaceful protests against the regime, but the conflict has transformed into a civil war. Activists say 19,000 people have been killed.

As the fighting grinds on, Syria reached out to its powerful ally Russia yesterday. Senior Syrian officials pleaded with Moscow for financial loans and supplies of oil products - an indication that international sanctions are squeezing Mr Assad's regime.

Syria is thought to be burning quickly through the 17 billion US dollars in foreign reserves that the government was believed to have at the start of Mr Assad's crackdown.

Deputy Prime Minister Qadri Jamil, who has led a delegation of several Cabinet ministers to Moscow over the past few days, told reporters yesterday that they requested a Russian loan to replenish Syria's hard currency reserves, which have been depleted by a US and European Union embargo on Syrian exports.

Russia has protected Syria from UN sanctions and continued to supply it with weapons throughout the conflict. The Kremlin, backed by fellow veto-wielding UN Security Council member China, has blocked any plans that would call on Mr Assad to step down.

Today, China said the West should be blamed for obstructing diplomatic and political efforts to restore order and peace in Syria.

Wang Kejian, a deputy director of North African and West Asian affairs at the Chinese Foreign Ministry, told a news conference that Western countries had hindered and sabotaged the political process by advocating regime change.

He reiterated China's stance that the solution to the Syria crisis should be a political one and that it is opposed to any military intervention.