Beirut (AFP) - US-led coalition air strikes on two Syrian provinces targeting jihadists have killed 472 civilians over the past month, a monitor said Friday, more than double a previous 30-day toll.

The Syrian Observatory for Human Rights said the period between May 23 and June 23 saw the highest civilian death toll in coalition raids for a single month since they began on September 23, 2014.

Observatory head Rami Abdel Rahman said 222 civilians, including 84 children, were killed in the largely Islamic State group-held province of Deir Ezzor.

Another 250 civilians, including 53 children, were killed in Raqa province, where US-backed forces are trying to oust IS jihadists from their bastion Raqa city.

He told AFP that the new deaths brought the overall civilian toll from the coalition's campaign to 1,953, including 456 children and 333 women.

The previous deadliest 30-day period was between April 23 and May 23 this year that cost 225 civilian lives.

The coalition insists it takes every measure to avoid hitting civilians, including by aborting missile strikes at the last moment if a civilian unexpectedly wanders into the target zone.

A statement emailed to AFP by the international alliance said its forces "work diligently and deliberately to be precise" in their air strikes.

"Our goal is always for zero civilian casualties," the statement said.

In its most recent report on civilian casualties, released June 2, the coalition said it had "unintentionally killed" 484 civilians in both Iraq and Syria.

But observers say the number is much higher.

Last month, US Defence Secretary Jim Mattis said President Donald Trump had instructed the Pentagon to "annihilate" IS in Syria in a bid to prevent foreign fighters from returning home.

Trump, who campaigned on a pledge to quickly defeat IS, signed an executive order soon after taking office giving his generals 30 days to come up with a revised plan to wipe the jihadists out.

The review resulted in the new "annihilation campaign" and saw commanders gain greater autonomy to make battlefield decisions.

A total of more than 320,000 people have been killed since Syria's conflict erupted in 2011 with anti-government protests, according to the Britain-based Observatory.