BEIRUT: Airstrikes on the northern Syrian city of Raqqa on Saturday killed at least 39 people and wounded many others in an intensified bombardment of the Islamic State group's de facto capital.

The Britain-based Syrian Observatory for Human Rights said 39 people were killed, including five children and seven women, when the air raids hit several areas in the city, which has been held by the extremists since 2013.

It was not immediately clear what country's warplanes carried out the airstrikes but such confusion is common in the immediate aftermath of raids.

The anti-Islamic State activist group Raqqa is Being Slaughtered Silently said the airstrikes were by Russian warplanes, adding that they have killed 43 civilians and wounded about 50 others.

A third opposition monitoring group, the Local Coordination Committees said the air raids were carried out by Syrian government warplanes, adding that dozens were killed or wounded.

The three groups said the air raids struck near the national hospital, a former army base and other neighborhoods.

Russia has been conducting air raids in Syria since September 30, even though Russia this week drew down its military presence in Syria after President Vladimir Putin ordered a partial pullout of Russian aircraft and forces from Syria, in support of indirect peace talks in Geneva.

On Thursday, Putin said Moscow would keep enough forces in Syria to continue the fight against the Islamic State group, the Nusra Front and other extremist organizations.

The Islamic State group is not included in the truce that was brokered by Russia and the U.S. that went into effect on Feb. 27 and led to a drop of violence in Syria.

The air raids come at a time when IS has lost large swaths of territory in northern Syria, including in Raqqa province, in battles with the US-backed predominantly Kurdish Syria Democratic Forces.

To the south, Syrian troops are on the offensive in an attempt to capture the ancient town of Palmyra, which has been under IS control since May.

The Observatory and the LCC reported airstrikes on the town that is home to some of the world's most precious archaeological sites. Several of those sites have already been damaged or destroyed by the extremists.

The Observatory said seven IS fighters were killed in the airstrikes on Palmyra on Saturday.

IS, which in June 2014 declared a caliphate in areas it controls in Syria and Iraq, has been under pressure in Iraq as well over the past few months.

The United States estimates that as of February, IS fields 19,000 to 25,000 fighters in Iraq and Syria — down from an estimated 20,000 to 31,500 frontline fighters — a number that was based on intelligence reports from May to August 2014.

A US official, who spoke on condition of anonymity to discuss the estimates, said the decrease reflects the combined effects of battlefield deaths, desertions, internal disciplinary actions, recruiting shortfalls and difficulties that foreign fighters face traveling to Syria.

Syria's five-year civil war has killed more than 250,000 and displaced half the country's population.