Syrian state-run media says a rare US strike on government-backed troops in eastern Syria killed and wounded dozens of tribal fighters, calling it a new effort “to support terrorism”.

The US-led coalition said its action was in “self-defence”, citing a major attack on its allied forces and US advisers in Deir el-Zour province by at least 500 fighters, battle tanks, howitzers and mortars.

The overnight US attack on Wednesday, which is said to have killed about 100 people and 19 children, added another layer to the Syrian conflict that is once again plunging into a new and unpredictable spiral of violence.

A stronghold of Islamic State militants until late last year, the province also was the group’s main source of oil revenue.

US-backed Kurdish-led forces have been fighting for control of Deir el-Zour with rival Russian-backed Syrian troops that are reinforced by Iranian-supported militias.

In an email on Thursday to The Associated Press, Colonel Thomas F Veale said the coalition reported to the Russians the buildup of the pro-government forces in the area before the attack, and communicated with them during and after it.

Colonel Veale said they suspect the Syrian pro-government forces were trying to seize terrain from the US-backed forces liberated from IS militants last year, including major oil fields in the area.

The Russian Defense Ministry said the US airstrike wounded 25 pro-Syrian volunteers. It alleged the incident showed that Washington was not interested in fighting Islamic militants but wanted “to seize and hold Syrian economic assets”.

The US airstrike coincides with escalating violence in Syria.

Turkey, a NATO member, has been carrying out a military offensive to clear a US-backed Kurdish militia from in a northwestern border town, increasing tensions between Washington and Ankara.

The Syrian government also has been pressing its campaign in a rebel-held area near the capital of Damascus.

Activists have said at least 211 were killed since Monday in eastern Ghouta.

The US State Department said it was “extremely concerned” about growing violence in Idlib and the eastern Ghouta area. State Department spokeswoman Heather Nauert says there have been reports of new attacks in the last 48 hours killing “dozens” of civilians.

Ms Nauert said the US is supporting a UN call for a month-long “cessation of violence.” She says the goal is to allow humanitarian aid and medical care to flow to more than 700 civilians in eastern Ghouta.

Russia’s UN Ambassador Vassily Nebenzia says he will raise the US-led coalition’s deadly airstrike on Syrian government-backed troops during closed consultations later on Thursday in the UN Security Council.

Meanwhile, Turkish officials said the leaders of Turkey, Russia and Iran will meet in Istanbul to discuss peace efforts for Syria.

– AAP