Syria war: US airstrike on Syrian troops threatens ceasefire deal, Russia says

The US State Department has expressed 'regret' over airstrike near Isis stronghold that killed 62 Syrian army soldiers

File photo of Samantha power the US Ambassador to the United Nations (AP)

A US-coalition led airstrike that hit a Syrian army base has put a "very big question mark" over the current ceasefire, the Russian Ambassador to the UN has said.

American coalition led strikes near Isis territory in the east of Syria accidentally hit Syrian army positions instead, a US official confirmed late on Saturday night. The operation was halted when the mistake was realised.

The US and Russian brokered cessation of hostilities in Syria's civil war, which began last Monday, is mostly holding up, with no civilian deaths reported by rights groups or monitors.

"Syria is a complex situation with various military forces and militias in close proximity, but coalition forces would not intentionally strike a known Syrian military unit," a State Department official said.

Russia, a close ally and military backer of the Syrian government, asked for an emergency council meeting at the United Nations, saying that if the bombing was a mistake, it is evidence of the US's “stubborn refusal” to co-ordinate military action with Moscow in Syria's civil war.

US envoy to the UN Samantha Power criticised the call on Saturday, accusing Russia of hypocrisy and "pulling a stunt". During the heated council meeting Power and her Russian counterpart, Vitaly Churkin, walked out while the other was speaking.

Calling Ms Power's remarks an "extraordinary display of American heavy-handedness", Mr Churkin implied the American response to the incident could endanger the fragile ceasefire.

"If what Ambassador Power has done today is any indication of their possible reaction then we are in serious trouble," he said.

Moscow said that 62 soldiers were killed in the bombing near Deir-ez-Zour, which the Syrian army called “blatant and dangerous aggression”. The UK-based Syrian Observatory for Human Rights said more than 80 died, and that Russian jets had been conducting strikes in the area at the same time.

Isis claimed they gained “complete control” over Jebel Tharda near Deir-ez-Zour airport in the ensuing chaos, but both Russian and Syrian state media have said all lost positions were recaptured in a matter of hours.

The terror group has control of Deir-ez-Zour city and much of the surrounding area.

The US-led coalition has been conducting air strikes against Isis since September 2014, and is also supporting rebel groups against President Bashar al-Assad elsewhere in the country.

Extremist groups Isis and Jabhat Fatah al-Sham, the Al-Qaeda affiliate operating in Syria, are not part of the current truce, and the seven-day ceasefire is supposed to lead to unprecedented joint US-Russian airstrikes against them.

Opening humanitarian corridors into the besieged city of Aleppo was also a key part of the ceasefire deal. Six days in, UN trucks are still at the Syrian-Turkey border waiting for permission from the Syrian government. Rebel groups inside the city are also reportedly blocking the route.

The US and Russia have disagreed over who is to blame for the hold up.