"The IS tried, starting late Saturday, to storm the air base. A total of 20 jihadists were killed in the attack, as well as two regime soldiers," the Syrian Observatory for Human Rights said on Saturday.

Nineteen of the IS members were Syrian, while one was Moroccan.

They were killed in fighting and heavy army shelling.

"The withdrawing jihadists seized and took with them several anti-aircraft missiles," said Observatory director Rami Abdel Rahman.

The attack was the second recent attempt by IS to take over the Deir Ezzor military air base, one of the last remaining regime positions in the eastern province.

Deir Ezzor is located on the border with Iraq, where IS also controls large swathes of territory.

The IS group emerged in Syria's conflict in the spring of 2013. Since then it has declared a "caliphate" straddling Syria and Iraq.

Activists say it rules the people under its control through a reign of terror.

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