"Dozens of Syrian soldiers captured while fleeing... after the ISIL overran Tabqa airbase were executed by the jihadists during the night," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights monitoring group.

The ISIL terrorists seized the airport on Sunday after weeks of bitter fighting with loyalist forces, cementing their control over Raqa province, capital of their self-declared "caliphate".

ISIL militants seized the Tabqa airbase on Sunday. Tabqa air base was the Syrian troops’ last stronghold in the area.

"It will facilitate attacks towards the north by the south Turkish borders," according to Laith Alkhouri, a senior analyst at New York-based intelligence consulting firm Flashpoint Global Partners.

The capture will likely allow ISIL to launch operations against rival rebel groups also fighting to oust the government of President Bashar Assad, Alkhouri said.

The base fell after a week of heavy fighting. "

Taking over the military airport was one of ISIL aims for a long time because of the heavy shelling and bombing from the airport toward Raqqa," he said.

According to the Syrian Observatory for Human Rights, at least 346 ISIL militants were killed and more than 170 government troops died since Tuesday in the battle over Tabqa, making it one of the deadliest confrontations between the two groups since the start of Syria's war.

NJF/NJF