US-led coalition air strikes on the Islamic State group's remaining territory in Syria's Raqa city killed 17 civilians on Wednesday, including children, a monitor said.

The coalition is providing air support in the form of heavy air strikes for the Syrian Democratic Forces (SDF) militia as it battles to oust IS from its onetime stronghold.

The Syrian Observatory for Human Rights, a Britain-based monitor, said the deaths on Wednesday followed two days of deadly strikes.

Since Monday, the monitor said, 38 civilians have been killed in US-led air strikes on the city.

Wednesday's deaths included five children, according to the monitor, which relies on a network of sources on the ground.

The coalition says it takes measures to avoid civilian casualties and investigates credible allegations of civilian deaths.

The United States has admitted that coalition strikes have killed 624 civilians in Syria and Iraq since 2014.

But rights groups and monitors say the figure is exponentially higher than that.

The SDF launched an operation to capture Raqa province from IS last year, and in June the militia broke into Raqa city for the first time.

It now holds more than half of the city, but the fighting has proved fierce and civilians have been killed both in the crossfire and while trying to flee.

Tens of thousands of people have fled Raqa, but the UN estimates between 10,000 and 25,000 civilians may still be trapped inside
source:AFP