At least 28 civilians have been killed by bombardment in the besieged Syrian opposition stronghold of Eastern Ghouta, near Damascus, most of them in Russian air raids, a monitor said.

At least 19 were killed in Russian strikes in the town of Misraba on Wednesday, while others died the same day in regime strikes and shelling in other areas, the Syrian Observatory for Human Rights said.

Seven children and 11 women were among those killed, according to the head of the Britain-based war monitor, Rami Abdel Rahman.

Victims were taken to a hospital in Douma, where an AFP correspondent saw rescuers bringing in mostly women and children.

Medical staff tried to revive an infant who had been pulled from the rubble, but without success. A young girl among the wounded received stitches for a serious injury to her face.

A medical source at the hospital told AFP: “Among the wounded were two women in their 20s. One of them lost both eyes and the other lost one eye.”

Eastern Ghouta, one of the last remaining opposition strongholds in Syria, is controlled mostly by rebels from the Jaish al-Islam group.

It has been under government siege since 2013, causing severe food and medicine shortages for around 400,000 residents.

According to the Observatory, Russian-backed regime forces have increased their bombardment of the enclave in recent days in response to militants and rebels attacking regime positions near the town of Harasta.

The monitor relies on a network of sources inside Syria and says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.

'Troops gathering'

The bombardment comes despite Eastern Ghouta being one of four “de-escalation zones” agreed by Russia, as well as regime backer Iran and rebel supporter Turkey, to help halt fighting around Syria.

Jaish al-Islam group leader Mohammed Alloush on Thursday accused the regime of preparing an assault on the opposition stronghold.

“The regime has been gathering its troops especially on our fronts for the past month to attack (Eastern) Ghouta,” he told AFP.

The Al-Watan newspaper, which is close to the government, on Thursday said the army was gathering its troops on the outskirts of Harasta.

The war in Syria has killed more than 340,000 people and displaced millions from their homes since it began in 2011 with the brutal repression of anti-government protests.

The latest raids came after at least seven civilians, including five children, were killed Tuesday by air strikes in northwestern Idlib province, the last outside government control, the Observatory said.

Two Russian servicemen killed

Government and allied forces backed by Russian warplanes have been battling fighters and rebels for more than a week in an area straddling the boundary between Idlib and Hama provinces.

The government push on the edge of Idlib province — also a “de-escalation zone” — follows two months of sporadic fighting that the United Nations says has displaced more than 60,000 people.

Russia first launched bombing raids in 2015 in support of Syrian President Bashar al-Assad's forces. The strikes have helped Assad regain control over much of the war-ravaged country.

Russia's defence ministry on Thursday said two servicemen were killed in a mortar attack by militants at the Hmeimim airbase in northwestern Syria on New Year's Eve, but denied media reports seven military planes were destroyed.

The news came a day after the ministry announced a Russian helicopter crash that killed two pilots following a technical fault as it was flying to Hama, in northwestern Syria, also on December 31.

Russia's Defence Minister Sergei Shoigu last month said the military had completed the partial withdrawal from Syria ordered by President Vladimir Putin, but Moscow would maintain a presence in the country, including three battalions and two bases.

Moscow acknowledged in recent months that its special forces are also active on the ground in the offensive against Islamic State group militants.