At least 472 civilians, including 137 children, have been killed during the past month of US-led coalition air raids in Syria, a monitoring group said.

The Syrian Observatory for Human Rights (SOHR) said on Friday 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.

The UK-based monitor said the deaths were mainly in the provinces of Deir Az Zor and Raqqa. The city of Raqqa is the self-declared capital of the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group in Syria.

The SOHR's head, Rami Abdel Rahman, said the fatalities included 222 civilians in Deir Az Zor, in eastern Syria, and 250 others in the northeastern governorate of Raqqa.

"This is the highest civilian death toll in the US alliance air strikes since they [the coalition] began bombing in the country on September 23, 2014," Abdel-Rahman said.

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The latest toll brought the number of civilian deaths from the US-led air raids in Syria to 1,953, he said.

The US-led coalition told the AFP news agency in a statement that its forces "work diligently and deliberately to be precise" in their air raids.

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

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

Hundreds of thousands of people have been killed since Syria's conflict erupted as an unarmed uprising against the rule of President Bashar al-Assad in March 2011. It has since escalated into a full-on armed conflict between government forces and rebel groups.

Source: Al Jazeera and news agencies