Baghdad (AFP) - At least 250 US-led air strikes have pounded the Syrian city of Raqa and surrounding territory in the past week, the coalition fighting the Islamic State group said Tuesday.

Coalition spokesman Colonel Ryan Dillon told AFP that the air raids targeted the greater Raqa area.

Activists and monitoring groups have reported that intensifying coalition bombardment of the city has left scores of civilians dead.

The Britain-based Syrian Observatory for Human Rights said at least 42 civilians had been killed in US-led strikes on Raqa Monday, taking the civilian toll for the past eight days to 167.

Dillon told AFP that the allegations would be taken seriously and investigated.

Since a US-backed offensive ousted IS from Mosul in neighbouring Iraq in July, the coalition has had more available aircraft to strike Raqa, he added.

"We have increased our strikes recently especially since the end of the Mosul battle," Dillon said.

Earlier this month, the coalition acknowledged the deaths of 624 civilians in its strikes in Syria and Iraq since 2014, but rights groups say the number is much higher.

The international alliance says it takes all possible measures to prevent unnecessary deaths.

"The avoidance of civilian casualties is our highest priority when conducting strikes against legitimate military targets with precision munitions, unlike the indiscriminate nature of ISIS tactics which result in an enormous number of avoidable civilian deaths," the coalition told AFP in an emailed statement on Tuesday.