Syrian warplanes hammered Damascus on Monday with loud explosions shaking the capital on the fourth day of a Muslim holiday marked by the failure of a ceasefire bid, an AFP correspondent said.

The explosions, which appeared to come from several different districts, could be heard over about two hours and were among the most intense in the city since the beginning of the 19-month conflict.

The Syrian Revolution General Council, a network of opposition activists on the ground, said the air strikes were northeast of the capital in and around the suburb of Harasta, a rebel stronghold.

Clashes broke out in Harasta, as three civilians were killed in shelling and gunfire in the nearby town of Douma, another opposition bastion, said the Syrian Observatory for Human Rights.

Overnight, troops pounded rebel positions in the outer southern district of Al-Hajar Al-Aswad, as explosions were heard in the nearby Qadam neighbourhood, where clashes erupted, it said.

In the northern metropolis of Aleppo, where fighting has raged since mid-July, sporadic clashes took place overnight across the city, said the Observatory, which relies on a countrywide network of activists, lawyers and medics in civilian and military hospitals.

Elsewhere in Aleppo province, two men were killed in shelling on the town of Hayan, while the army also bombarded the towns of Kfar Hamra and Aandan, the Observatory said.

Warplanes also shelled a village in the northwestern province of Idlib near Maaret al-Numan, which rebels seized on October 9, cutting off a key army supply line on the Damascus-Aleppo highway.

The Observatory also reported that 14 soldiers were wounded in fierce clashes with rebels outside the Wadi Daif military base, near Maaret al-Numan.

The violence followed a day in which 134 people -- 51 civilians, 35 soldiers and 48 rebels -- were killed nationwide on Sunday.

The Syrian uprising, which began in March 2011 as a peaceful movement, has steadily militarised after being met with brutal state repression and has left more than 35,000 people dead, according to rights groups.

Most rebels, like the population, are Sunni Muslims in a country dominated by a minority regime of Alawites, an offshoot of Shiite Islam.