At least four people were killed in a drone strike targeting Iran-backed groups in government-held eastern Syria on Wednesday, a war monitor said.

"Four people were killed and eight wounded in a drone strike near a weapons factory belonging to Iran-backed groups and near a truck loaded with weapons," Rami Abdel Rahman of the Syrian Observatory for Human Rights told AFP.

There was no immediate word on who carried out the strike in the eastern city of Deir el-Zour.

It targeted a part of the city that is home to residences of top Iranian commanders and senior officers of Lebanon's Hezbollah movement, as well as an Iranian hospital to treat cholera patients, Abdel Rahman said.

Pro-Iran factions aligned with the Syrian government, including Hezbollah, are heavily deployed south and west of the Euphrates River which runs through Deir el-Zour province.

Wednesday's attack followed a series of unclaimed drone strikes on Jan. 30 that targeted a suspected Iranian weapons convoy in the province and killed 11 people, including a pro-Iranian commander, the Observatory said.