MOSCOW – Fifteen Russians employed in Syria by a private security companywere killed when an unexplained explosion rocked an arms depot at theirbase in the war-torn country, a monitor said Wednesday.

The incident happened at the company’s weapons storage facility at TabiyaJazira a few days ago in the northeastern province of Deir Ezzor, said theBritain-based Syrian Observatory for Human Rights.

Observatory directory Rami Abdel Rahman said the company in question was incharge of “protecting the oil and gas fields controlled by the Syrianregime”.

“Fifteen Russians working for a Russian private security company werekilled in an explosion at a weapons depot of the company in Tabiya Jazirain Deir Ezzor province,” he told AFP.The gas field

Seven other people, mostly pro-regime Syrian fighters, died in the blast,he added. The Russian workers had been at the site when “regime forces weretrying to take the Coneco gas field” controlled by the Syrian DemocraticForces (SDF), a US-backed alliance of Arab and Kurdish fighters.

Their reported deaths come after the US-led coalition against jihadistsstruck the Coneco plant on Thursday in retaliation for an attack on an SDFbase near the gas field on the eastern bank of the Euphrates river.

The US-led coalition said Thursday it killed at least 100 pro-regimefighters to fend off an attack on its allies in eastern Syria, in one itsdeadliest confrontations yet with forces backing Damascus.

The Observatory, which relies on a network of sources on the ground inSyria, said 45 pro-regime fighters were killed. The government of SyrianPresident Bashar al-Assad denounced the strikes as a “war crime”.