Damascus, Mar 25 (IANS): US airstrikes on strongholds of pro-Iran militias in eastern Syria killed 11 fighters, a war monitor reported.

The airstrikes hit an arms depot and other military outposts of the pro-Iran fighters in the province of Deir al-Zour, in retaliation to the pro-Iran militias' drone attacks on US positions in the same region, according to the Syrian Observatory for Human Rights, a Britain-based war monitor on Friday.

Rami Abdul-Rahman, the head of the observatory, said the Iranian fighters had targeted US positions in the al-Omar oil field in Deir al-Zour overnight, adding that both sides exchanged fire, Xinhua news agency reported.

Abdul-Rahman added he expected the US would carry out more attacks after recruiting agents on the ground to gather information about the locations and positions of the pro-Iran militias in eastern Syria.

The Syrian government has not commented on the most recent escalation.

The Pentagon said on Friday that a US contractor was killed, and five US service members and one other US contractor were wounded when a suspected Iranian drone struck a facility of the US coalition in northeast Syria.