Two rockets targeted a US patrol base in northeastern Syria late Friday, the third such attack in nine days, US Central Command said.

Centcom did not indicate who fired the rockets but said, in a statement, that they aimed at "coalition forces at the US patrol base in Al-Shaddadi, Syria".

The strike at about 10:30 pm (1930 GMT) caused no injuries or damage to the base or coalition property, said Centcom, which covers the Middle East region.

The US troops support Syrian Democratic Forces (SDF), which are the Kurds' de facto army in the area and led the battle that dislodged the Islamic State group (IS) from the last scraps of their Syrian territory in 2019.

Hundreds of American troops are still in Syria as part of the fight against IS remnants.

"Syrian Democratic Forces visited the rocket origin site and found a third unfired rocket," Centcom added in its latest statement.

On November 17 rockets targeted the coalition's Green Village base which is in Syria's largest oil field, Al-Omar, near the Iraqi border, Centcom said at the time. There were no injuries.

A war monitor, the British-based Syrian Observatory for Human Rights which has a wide network of sources in Syria, said that strike came from "a base of pro-Iranian militias".

Such groups have significant influence in the Syria-Iraq border region.

In another attack, a Turkish drone strike on Tuesday killed two SDF fighters and posed "a risk to US troops", Centcom told AFP earlier.

That strike hit a base north of Hassakeh city, also in Syria's northeast but farther north.

On November 20 Turkey announced it had carried out a series of air and drone strikes in Iraq and Syria, a week after a bomb attack in Istanbul that killed six people and wounded 81.

Turkey says it is targeting rear bases of the Kurdistan Workers' Party (PKK), designated as a terrorist group by the European Union and the United States, and the Syrian Kurdish People's Protection Units (YPG), which dominate the SDF.

Both Kurdish groups denied responsibility for the Istanbul attack.