Air strikes believed to have been carried out by Russian warplanes on an ISIS group-held town in central Syria killed 23 civilians, a monitoring group said on Wednesday.

Among those killed in the Monday strikes on the Homs province town of Al-Qaryatain were three children and a woman, the Syrian Observatory for Human Rights said.

The Britain-based group had earlier reported at least 10 people killed in apparent Russian strikes on the town on Monday.

It said ISIS fighters were also believed to have been killed in the strikes, but had no confirmed figure.

ISIS seized Al-Qaryatain in August, kidnapping several hundred civilians.

The group has also destroyed an ancient monastery in the town, which was once seen as a symbol of coexistence in Syria.

The Observatory relies on a network of sources on the ground in Syria, including opposition activists and individuals in government-held territory.

The group says it distinguishes between strikes carried out by Syrian, Russian and US-led coalition aircraft based on flight patterns indicating whether planes took off from inside the country, as well as the type of planes and ordnance used.

Russia began its air campaign in support of ally President Bashar al-Assad on September 30, saying it was targeting the ISIS group and other "terrorists".

But rebels and their backers accuse Moscow of focusing largely on moderate opposition forces rather than ISIS.

According to the Observatory, the first month of Russian strikes killed nearly 600 people, two-thirds of them fighters.

The rest - some 185 - were civilians, it says.

A US-led coalition that has been bombing ISIS targets in Syria since September 2014 has killed 3,649 people, according to the Observatory.

It says 226 of those, around six percent, have been civilians.

More than 250,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011.