The Nour al-Din al-Zenki Movement, a Syrian opposition group, claimed that a Russian warplane targeted Idlib province’s Benin village using a white phosphorous bomb.

Yasser al-Yousef, an activist in the movement, told Anadolu Agency late Thursday that the attack left a number of people wounded, but he did not give an exact number or say when the alleged event took place.

White phosphorus is typically used to produce a camouflaging smoke. When used directly as a weapon, it burns flesh. It is forbidden to be used indescriminately against civilians.

While the Kremlin says its air campaign is aimed at supporting the Assad regime against Daesh, many NATO members say Russia is targeting mainstream opposition groups opposed to Assad, several of which enjoy the support of the U.S. and its allies.

At least 250,000 people have been killed since the Syria conflict began in 2011, with 7.6 million internally displaced and over four million having fled to other countries.