The Kremlin on Wednesday denied involvement in air strikes on Syria's rebel-held Eastern Ghouta enclave that monitors say have killed at least 250 civilians since the start of the week.

"These are groundless accusations. It is not clear what they are based on. No specific data has been given. We do not agree (with them)," said presidential spokesman Dmitry Peskov in response to a US briefing saying that Russia was responsible for the attacks.

The Britain-based Syrian Observatory for Human Rights has also blamed Russian warplanes for the strikes.

Bombardment of the enclave on the outskirts of Damascus on Tuesday killed 106 civilians, including 19 children, the Observatory said.

It was the second straight day that the civilian death toll topped 100, after 127 were killed Monday in Eastern Ghouta's bloodiest day in four years.

The strikes left an important hospital out of action, further limiting the little medical aid accessible to besieged civilians.

The rebel-held region is nominally included in a "de-escalation" deal meant to tamp down violence, but President Bashar al-Assad appears to be preparing troops for a ground assault to retake it.

The Russian military has fought a campaign for over two years in Syria, launched in September 2015 in support of Assad, helping to turn around the multi-front war.

Russia, Iran must help end 'massacre' in Syria enclave: Berlin
Berlin (AFP) Feb 21, 2018 –

Germany on Wednesday urged Russia and Iran to push the Syrian regime to end the deadly airstrikes on rebel-held Eastern Ghouta, noting that the two had pledged to be guarantors of peace in Syria.

"One has to ask where is Russia, where is Iran, which had pledged in Astana to guarantee a ceasefire also in Eastern Ghouta," said Steffen Seibert, spokesman for Chancellor Angela Merkel, referring to peace talks in the Kazakh capital.

"Without the support of these two allies, Assad's regime would not be where it is today, and undoubtedly, without this support, this regime would have to show more readiness to negotiate in the UN (peace) process," the German government spokesman added.

"We demand that the Assad regime immediately end the massacre in Ghouta and allow in humanitarian aid as well as medical evacuation. We also demand that the backers of the Assad regime use their strong influence to achieve this end," Seibert said.

The regime of Syrian President Bashar al-Assad stepped up its airstrikes this month on the rebel enclave east of Damascus, where close to 300 civilians have been killed since Sunday.

Warplanes continued to pound Eastern Ghouta towns on Wednesday, killing 24 civilians, according to the Syrian Observatory for Human Rights.