The Syrian Observatory for Human Rights said the strikes between April 23 and May 23 killed a total of 225 civilians in the country.
US-led air strikes on Syria killed a total of 225 civilians over the past month, a monitor said on Tuesday, the highest 30-day toll since the campaign began in 2014.
Britain-based war monitor, the Syrian Observatory for Human Rights (SOHR) said the civilians died between April 23 and May 23 and included 44 children and 36 women.
The US-led air campaign against Daesh in Syria began on September 23, 2014. According to the group these air raids by the International Coalition has claimed the lives of 7,986 people - civilians and combatants combined - since they began operations.
The International Coalition consists of the United States, United Kingdom, France, Germany, Italy, Canada, and Denmark among others.
Highest monthly civilian death toll
"The past month of operations is the highest civilian toll since the coalition began bombing Syria," SOHR's head Rami Abdel Rahman said.
"There has been a very big escalation," Rahman added.
The past month's deaths brought the overall civilian death toll from the coalition's campaign to 1,481, including 319 children, SOHR said.
The US military said in May that coalition air strikes in Syria and Iraq had "unintentionally" killed 352 civilians since operations against Daesh began.
The strikes between April 23 and May 23 also killed 122 Daesh members and eight fighters loyal to the Syrian regime, the Observatory said.