WASHINGTON (Reuters) - The U.S. military said late on Saturday that unidentified forces had fired a missile at a base hosting U.S. and local partner forces in Syria, but it caused no casualties or damage.

The army added in a brief statement that the 107mm missile had no effect inside the base located in northeastern Syria.

"Additional missiles were found at the launch site," said the US military's Central Command, which oversees US forces in the Middle East.

Central Command did not say who it believed was responsible for the failed attack.

This comes just two days after an unusual US helicopter air strike on a government-held village in northeastern Syria killed an Islamic State member on Thursday. Hours later, another US air strike took place, killing two more members of the organization.

US forces first deployed to Syria during the Obama administration's campaign against the Islamic State, in partnership with a Kurdish-led group called the Syrian Democratic Forces. About 900 US troops are deployed in Syria, most of them in the east.

However, Washington has accused Iran-backed militias of carrying out attacks on US forces in recent months. Those Iranian-backed militias established themselves in Syria as they fought in support of President Bashar al-Assad during the Syrian civil war.