DAMASCUS, Nov. 20 (Xinhua) -- At least 16 Islamic State (IS) militants were killed Tuesday by intensive U.S.-led airstrikes on IS-held areas in eastern Syria, a war monitor group reported.

The fresh strikes targeted the town of Hanin, one of the towns in the last IS-held pocket in the eastern countryside of Deir al-Zour province in eastern Syria, according to the Syrian Observatory for Human Rights.

The Britain-based watchdog group said 640 IS fighters have been killed since the U.S.-led operation on the eastern bank of Euphrates River started on Sept. 10.

U.S.-led airstrikes on the last IS-held pocket on the eastern bank of Euphrates River have recently intensified as the U.S.-backed Kurdish militias such as the Syrian Democratic Forces were planning a second wave of attacks on the IS after a failed attempt on Sept. 10.

The strikes have also led to civilian casualties, with the state news agency SANA saying that as many as 100 civilians had been killed last week in U.S.-led airstrikes in eastern Syria.