Syria ruins
© Ammar Abdullah / Reuters
Russia's Permanent Representative to the UN, Vitaly Churkin, has hit out at Washington's decision to freeze all cooperation with Russia over Syria, in the wake of a series of diplomatic setbacks.

"I don't think there is any alternative [to the bilateral ties between Moscow and Washington]," the diplomat told Russian reporters in New York. "That they have announced this is highly regrettable."

"There is also no alternative to trying to implement a ceasefire, and to stopping the Al-Nusra Front and ISIS while making sure that the so-called moderate opposition understands that time has come to lay down their weapons."

Following months of negotiations and stillborn peace deals, on Monday the US said that Russia was "unwilling or unable" to ensure that the Syrian government stuck to them, and claimed that Moscow and its allies in Damascus "have chosen to pursue a military course."

Moscow does not accept responsibility for the breakdown in cooperation, and says it has done everything to sustain the peace process, including implementing a 72-hour ceasefire late last month that should have ensured the delivery of humanitarian aid to Aleppo, the site of the most intense fighting between government forces and opposition factions.

Russia also says that the White House kept covering up for extreme Islamists, making it impossible to produce a joint plan of operations, a key part of the bilateral proposal agreed a fortnight ago.

"Why could Washington not deliver what it promised - to delineate between the terrorists [the Al-Nusra Front] and the so-called moderate opposition," said Russian Foreign Ministry spokesperson Maria Zakharova.

United Nations Syria envoy Staffan de Mistura said that his organization "deeply regrets" the communication breakdown between Moscow and Washington, and promised to continue working on a diplomatic resolution to a war that has resulted in over 400,000 deaths, according to the UN's own estimate.

"The UN will never abandon the Syrian people to a destiny of endless violent conflict," de Mistura said in a statement.