Syrian rebels have killed at least 70 regime-aligned soldiers attempting to retake the rebel-held enclave of Eastern Ghouta in a ground offensive.

The opposition forces clashed with the government troops on Sunday as Damascus regime continued its deadly bombardment of Eastern Ghouta, news website al-Modon reported.

Seventy regime troops were killed and two were taken captive in fighting along the perimeter of the rebel-held suburb of the Syrian capital, according to the report.

The cornered rebels have also been firing back into Damascus, where six civilians were wounded on Saturday, state media said, with around 20 people have been killed in eastern districts of the capital since last Sunday.

Meanwhile, the civilian death toll in Eastern Ghouta from seven days of intense bombing has reached more than 500.

The United Nations secretary-general on Monday demanded the immediate implementation of a 30-day ceasefire.

UN chief Antonio Guterres praised the adoption of a Security Council resolution on Saturday calling for the truce but underscored "Security Council resolutions are only meaningful if they are effectively implemented".

Fresh bombardment by the regime killed at least 10 civilians in Eastern Ghouta on Monday, including nine members of a same family, the Syrian Observatory for Human Rights monitor group said.

Airstrikes destroyed a building in Douma, the main town in the Eastern Ghouta area east of Damascus, and buried alive an entire family, according to the Observatory.

The Observatory said that a child died and at least 13 other people suffered breathing difficulties in a suspected chemical attack on Eastern Ghouta on Sunday.

Rebels accused Damascus of using chlorine gas, but Moscow, a staunch ally of President Bashar al-Assad's regime, accused his opponents of using "toxic substances" to make it appear that they had been deployed by regime forces.

Damascus, which has repeatedly denied using chemical weapons, has been accused of several chlorine gas attacks in recent weeks, including two in January in Eastern Ghouta.