An arms dump has exploded in Deir Ezzor province in Syria, killing 25 Islamic State (IS) militants, according to the Syrian Observatory for Human Rights (SOHR), a UK-based activist group.

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.

The group says the crossing at southern Quneitra was seized by fighters from the Ahrar al-Sham alliance, which has been fighting IS-linked rebels as well as forces loyal to the government of Syrian President Bashar al-Assad.

Ahrar al-Sham is part of a broader alliance of rebels that recently captured the town of Jisr al-Sughur in north-western Syria, consolidating their hold over Idlib province.

Jisr al-Sughur has been under government control since the early stages of the conflict. In June 2011, large protests against the regime led to the deaths of 120 troops in circumstances disputed by the government and its opponents.

BBC