At least 25 Daesh militants were killed in an explosion in Deir ez-Zor governorate in eastern Syria, the London-based Syrian Observatory for Human Rights said Thursday.

The cause of the blast, that targeted a Daesh factory for making explosives, has not been yet known.

More than 20 militants were injured in the blast, it said.

The death toll is likely to increase as there are many critical conditions among the wounded.

Daesh militant group laid its control over Deir ez-Zor governorate last summer after battles with the government forces and other militant groups in the area.