DAMASCUS, Feb. 26 (Xinhua) -- U.S. military air strikes in eastern Syria have killed at least 22 pro-Iran fighters before daybreak Friday, a war monitor said.

The Syrian Observatory for Human Rights said the fighters were killed when the strikes hit a shipment of weapons belonging to Iraq's Hashed al-Shaabi force and the Iraqi Hezbollah group.

The strikes were carried out as the shipment from Iraq was entering into Syria through the al-Qaem border crossing in Syria's eastern province of Deir al-Zour, the watchdog group said, adding that the death toll is likely to rise considering the number of critically wounded fighters.

Syrian state media reported the attack but have not provided more information so far.

The Pentagon confirmed earlier that the U.S. military had conducted airstrikes against infrastructure utilized by Iranian-backed militant groups in eastern Syria, the first to hit the Middle East country since the arrival of the Joe Biden administration.