Airstrikes by Russian warplanes on the ISIL-held Syrian city of Raqqa killed 42 people earlier this week, including 27 civilians, the Syrian Observatory for Human Rights said on Friday.

Fifteen Islamic State in Iraq and the Levant fighters accounted for the remainder of the death toll, the British-based Observatory said, after a series of strikes on Tuesday that hit the ISIL stronghold.

The bombings add to a civilian death toll from Russian strikes, which the Syrian Network for Human Rights, another monitoring group, said on Monday stood at 254 people killed in just over a month.

It was a rare heavy Russian bombardment targeting ISIL rather than other insurgent groups.

Russia's air force intervened in Syria's four-year civil war on Sept. 30 on the side of President Bashar al-Assad, launching a campaign it said targeted ISIL. The United States says Russian raids have mostly hit other Syrian insurgents, including foreign-backed and more moderate groups.

The Russian intervention marks in a new phase in the war, intensifying fighting in the country's west and northwest between rebels and pro-government forces also backed by Iranian troops and Lebanese Hezbollah fighters.

Russian strikes have hit ISIL-held areas farther east but have mostly been in the west. Its air force said on Tuesday it has flown 1,631 sorties and struck 2,084 targets since the start of the campaign.

More than 120,000 people have been driven from their homes since Moscow's bombing started in Syria, the United Nations says.

The war has killed an estimated 250,000 people and driven more than 11 million from their homes.

Wire services