The U.N.'s children agency is condemning the killing of children amid Syria's ongoing civil war following brutal incidents in the country's north.

In a statement distributed Thursday, UNICEF says dozens of children were among those killed in and around the town of Manbij, where airstrikes blamed on the U.S.-led coalition killed scores of people in the past few days.

The coalition has not commented on the accusations and has stepped up its airstrikes on the area, which is controlled by the Islamic State group.

UNICEF says "no matter where they are in Syria or under whose control they live - absolutely nothing justifies attacks on children."

UNICEF also condemns the killing of a 12-year-old boy who was beheaded on-camera in Aleppo this week by Syrian rebels.