"Russian aviation is not striking residential areas of Eastern Ghouta and especially it is not using incendiary weapons, unlike the US-led international coalition," the Russian defence ministry said in a statement.

"The statements that swindlers speculating on human grief -- the White Helmets as well as Britain's so-called the Syrian Observatory for Human Rights -- are spreading are glaring lies," the statement said, quoted by TASS state news agency.

The Syrian Observatory for Human Rights said earlier Friday that Russian air strikes killed 37 civilians in the Arbin area of the shrinking rebel enclave of Eastern Ghouta near Damascus overnight.

"Russian air strikes and incendiary weapons killed the civilians in a basement from burning or suffocation" late on Thursday before a ceasefire came into effect in the area, Observatory head Rami Abdel Rahman said.

The Britain-based Observatory says it relies on flight patterns, aircraft involved and ammunition used to determine who carries them out.

The White Helmets, a civil defence organisation operating in rebel-held areas, said most of the dead were women and children.

More than 1,600 civilians have died in Eastern Ghouta since the regime launched a blistering assault on the last rebel bastion near Damascus on February 18, the Observatory says.