Washington's 'unintentional' bombing of a Syrian army position has got Moscow 'deeply worried' about the efficacy of the peace deal
The Syrian cease-fire appears near collapse after scores of Syrian soldiers loyal to President Bashar al-Assad were killed in a United States-led coalition air strike on Saturday.
One of the key tenets of the Syrian "cessation of hostilities" brokered by Washington and Moscow was to freeze all attacks on forces allied to either camps.
But the latest air strike, which killed at least 62 soldiers of the Syrian regime at Jebel Tharda near Deir al-Zor airport, has jeopardised the truce signed by the US and Russia.
Moscow called for an emergency UN security meeting with the US but that ended abruptly.
While Washington dubbed Moscow's request for the meeting as a "stunt", Russia said the US was violating the peace agreements.
The US, however, has apologised for the Saturday strike, saying they had intended to attack "Daesh (IS) fighting position".
The Pentagon said coalition forces "would not intentionally strike a known Syrian military unit".
But the latest development has got Moscow "deeply worried" about the continuation of the peace deal signed earlier this week.
The Syria cease-fire was signed by US and Russia on September 12, halting months of deadly violence in Syria.
"The actions of the pilots — if they, as we hope, were not taken on orders from Washington — fall between criminal negligence and direct pandering to IS terrorists," a statement from the Russian foreign ministry said, AFP reported.
Russia is also worried about US' inability to get all factions of Syrian rebels give their full backing to the cease-fire.
The US-allied Syrian rebels have agreed to "cooperate positively" to the peace deal but they have voiced their concerns about its long-term efficacy.
Meanwhile, government forces which are supported by Russia have launched a fresh offensive against Islamic State in the key airbase of Deir Ezzor, AFP quoted unnamed military sources as saying.
The Syrian government said the offensive was necessary as the truce has given IS time to recover and plan its next strikes.
The airbase is crucial as IS is using it to bomb Syrian army aircraft. On Sunday, IS claimed to have struck a Syrian plane close to Deir Ezzor, killing one pilot.
(WION with inputs from agencies)