A US F-15 over norther Iraq.
US-led air strikes hit grain silos and other targets in Islamic State-controlled territory in northern and eastern Syria overnight, killing civilians and wounding militants, a group monitoring the war said on Monday.
The aircraft may have mistaken the mills and grain storage areas in the northern Syrian town of Manbij for an Islamic State base, said the Britain-based Syrian Observatory for Human Rights. There was no immediate comment from Washington.
The United States has targeted Islamic State and other fighters in Syria since last week with the help of Arab allies, and in Iraq since last month. It aims to damage and destroy the bases, forces and supply lines of the al Qaeda offshoot which has captured large areas of both countries.
The strikes in Manbij appeared to have killed only civilians, not fighters, said Rami Abdulrahman, who runs the Observatory which gathers information from sources in Syria.
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"These were the workers at the silos. They provide food for the people," he said. He could not give a number of casualties and it was not immediately possible to verify the information.
Manbij sits between Aleppo city in the west and the town of Kobani on the northern border with Turkey, which Islamic State has been trying to capture from Kurdish forces, forcing tens of thousands of Syrian Kurds to flee over the frontier.
Syria's army also carried out air raids in Aleppo province overnight, targeting areas east of Aleppo city with barrel bombs and other projectiles, the Observatory said. The army also carried out air strikes in Hama in western Syria.
Forces loyal to President Bashar al-Assad have been battling Islamist fighters around Aleppo, which is held by a number of groups in Syria's war
In eastern Syria, US-led forces bombed a gas plant controlled by the Islamic State outside Deir al-Zor city, wounding several of the militant group's fighters, the Observatory said.
The United States has said it wants strikes to target oil facilities held by Islamic State to try to stem a source of revenues for the group.
The raid hit Kuniko gas plant, which feeds a power station in Homs that provides several provinces with electricity and powers oil fields generators, the Observatory said.
US-led warplanes also hit areas of Hasaka city in the north east and the outskirts of Raqqa city in the north, which is Islamic State's stronghold.