"There was an attack on the outskirts of the Khalkhalah military airport in Sweida province on Friday," said Rami Abdel Rahman, the head of the Syrian Observatory for Human Rights.

The forces loyal to President Bashar al-Assad had been able to maintain control over the airport and its surrounding areas despite losing 20 fighters.

At least 15 militants were killed. Although the Observatory was awaiting confirmation on the identity of the attackers, Abdel Rahman told reporters they were likely to have been jihadists from the Islamic State group.

Khalkhalah airport lies along a major highway that links the regime-held provincial capital of Sweida to Damascus.

"The area is important because it's Druze and borders Damascus province," Abdel Rahman told reporters, referring to the minority sect that considers Sweida its stronghold.

The regime of President Assad claims to protect Syria's minorities against foreign-backed Islamists.

But attacks on minority communities have increased with the rise of IS, which regularly targets such sects in Syria, as well as Sunnis who it alleges have violated its interpretation of Islam.

More than 215,000 people have been killed in Syria's four-year war, which is increasingly dominated by jihadist groups.

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