A large explosion in the town of Al-Mayadeen was followed by several smaller blasts, the group said.

It is not clear if the blasts were caused by an attack or by an accident.

Syria's civil war, which began four years ago, has killed more than 200,000 Syrians and displaced 11 million.

Much of Syria's eastern province of Deir Ezzor is under the control of IS. The militants last year also seized a broad belt of territory in northern Iraq.

The SOHR website said the explosions took place in an IS warehouse containing bombs.

Twenty militants were wounded in the blasts, the activist group said.

Meanwhile, a hardline Islamist rebel alliance has captured a Syrian border crossing near Israeli-occupied Golan Heights, the SOHR says.