It fell in the Conoco gas field in Deir Ezzor province, near a base of the US-led coalition battling Islamic State group remnants, said the Britain-based Syrian Observatory for Human Rights.

The war monitor said a blast was heard in the area but there were no immediate reports of casualties.

It said pro-Iran militias were likely responsible for the incident that followed a series of recent attacks on the nearby Al-Omar oil field, which also houses coalition forces.

The state-run SANA news agency said an explosion was heard from the area of the Conoco gas field, but did not provide additional details.

The coalition was not immediately available for comment.

The latest incident came amid heightened tensions following US strikes last month against three targets Washington said were used by pro-Iran groups in eastern Syria and western Iraq.

On Wednesday, Syrian Kurdish forces said they repelled drone attacks near a major coalition base at the al-Omar oil field.

Last Sunday, Kurdish forces said two unidentified rocket-propelled grenades landed on the western side of the al-Omar oil field, without causing casualties.

The Observatory blames pro-Iran militias for both attacks.

ho/ach