SYRIAN state-run media have confirmed a rare US strike on government-backed troops in eastern Syria, citing reports of dozens killed and wounded from the attack.

The overnight attack, which a US military official earlier said killed about 100, adds another layer to a conflict in Syria that is once again plunging into a new unpredictable spiral of violence.

The American official said the US launched the air strikes after as many as 500 attackers began what appeared to be a co-ordinated assault on US-backed forces known as the Syrian Democratic Forces (SDF) who were accompanied by US advisers in Deir el-Zour province.

The strikes were in self-defence after the pro-government forces began firing artillery and tank rounds at the SDF, according to the official. He added that about 100 of the attackers were killed.

It was a rare US strike against forces that support Syrian president Bashar Assad’s regime. Syria’s state media said the US-led coalition bombed government-backed troops in Khusham, a town in the oil-rich Deir el-Zour province, describing them as tribal fighters. The media cited reports of dozens killed and wounded.

The official state news agency SANA said the local fighters were battling Daesh militants and the US-backed SDF in the area. The agency labelled it an “aggression” and a “new massacre”.

The US-led coalition said in a statement that the attack took place eight kilometres (five miles) east of the Euphrates River de-confliction line. The US and Russia, which back rival forces in Deir el-Zour province, have kept in close contacts to avoid friction.

The statement suggested the coalition was calling out Russia on the assault, but it stopped short of actually laying the blame.

The Syrian Observatory for Human Rights, which monitors the war in Syria, said Deir el-Zour province continues to witness tensions following the foiled attack and the US response, and added that there were reports of new mobilisation to the area.

The observatory, which relies on a network of activists on the ground, said the Khusham area saw intense clashes with heavy weaponry late on Wednesday between pro-government forces and the SDF. The clashes are thought to have prompted the coalition response with land-to-land missiles and air strikes.

At least 45 pro-government fighters, which included Arab and Asian fighters, were reportedly killed.

Last summer, the US-led coalition shot down Iranian-made armed drones and aircraft affiliated with the Syrian government in southern Syria, after they came dangerously close to US-backed forces and advisers.

The US air strike coincides with escalating violence in Syria, with Turkey engaged in a military offensive against US-backed Kurdish militia from a north-western border town, increasing tensions between the US and its Nato ally Turkey.

Meanwhile, Turkish officials said Turkish, Russia and Iranian leaders will meet in Istanbul to discuss peace efforts for Syria.

The officials said that Turkish President Recep Tayyip Erdogan and his Russian Vladimir Putin agreed to the summit during a telephone call on Thursday. It was not immediately clear when the Istanbul meeting would take place.

The two leaders also reportedly agreed that efforts to create “observation posts” in Syria’s Idlib province as part of a “de-escalation” agreement between Turkey, Russia and Iran should gain momentum.

They discussed the humanitarian situation in the Ghouta region just east of Damascus, where dozens have been killed in aerial strikes in the past few days.