MOSCOW (AFP) – Russia’s two-and-a-half year dispute with the West over the conflict in Syria hit a new peak Monday as Moscow warned against military action without UN approval and cast doubt over the regime’s involvement in a claimed chemical weapons attack.

The alleged use of chemical weapons in an attack outside Damascus has driven a new wedge between Russia and the West, with Moscow and Western capitals offering vastly different interpretations of the incident.

Whereas Britain, France, Turkey and the United States have said the attack appears to have been perpetrated by the regime of Bashar al-Assad, Russia believes it was a ploy by rebels with the aim of discrediting the Kremlin’s traditional ally.

A telephone call Monday between Russian President Vladimir Putin and British Prime Minister David Cameron underlined how far apart Moscow and the West were.

Putin said that “they did not have evidence of whether a chemical weapons attack had taken place or who was responsible,” according to a Downing Street spokesman in London.

Cameron insisted that there was “little doubt” Assad’s regime had carried out a chemical attack, according to a readout of the conversation.

With clamor growing in Western states for military action against Assad, Russia warned such intervention would destabilize the entire Middle East and be based on false reasoning.

Any action such as air strikes would likely have no mandate from the UN Security Council, where Russia and its ally China would be almost certain to block resolutions approving force.

Britain — as well as staunchly anti-Assad Turkey — raised the prospect of a confrontation with Russia similar to that over the 2003 U.S.-led Iraq invasion or the 1999 Kosovo NATO air campaign by launching military action without UN approval.

“If force is used without a UN resolution it will lead to very serious consequences in relations between Russia and the United States and its NATO partners,” said Alexander Filonik, a Middle East expert at the Institute of Oriental Studies of the Russian Academy of Sciences.

At a hastily called news conference Monday, Russian Foreign Minister Sergei Lavrov said any use of force against Syria without UN approval would be a “very grave violation of international law.”

He said ideas floated in the West about knocking out the regime’s military infrastructure and helping hand victory to rebels were not just an “illusion” but a “grave mistake that will not lead to any peace, but only mark a new, even bloodier stage of the war in Syria.”

Taking military action against Assad would be a clear sign from the West that it does not want to take account of Moscow’s opinion, Maria Lipman of the Carnegie Center in Moscow told AFP.

“Moscow could not let that go by without a response,” she said, adding that Russia could hit back by strengthening military cooperation with the Assad regime.

The surge in tensions coincided with the appearance Monday in the Izvestia newspaper — one of the most slavishly pro-Kremlin media outlets in Russia — of a lengthy interview with Assad.

Assad used the interview to thank Russia for its support, ridicule as “nonsense” the idea that his regime used chemical weapons and warn the United States of failure if it attacked Syria.

“London and Washington… just need a guilty verdict [on Assad]. Any other verdict will be rejected,” the head of the lower house of Russian parliament’s foreign affairs committee, Alexei Pushkov, wrote on Twitter.

Russian officials are now comparing the possible use of force against Syria to the U.S.-led invasion of Iraq, which was vehemently opposed by Putin as based on flawed intelligence that Saddam Hussein’s regime possessed weapons of mass destruction.

The U.S. administration’s claims of weapons justifying the invasion at the time later proved false.

“There are many similarities in the tactics of the Western states in Iraq,” Filonik told AFP. “History is repeating itself.”

Russia has been chastened by its experience in the 2011 air campaign that ousted Libyan leader and longstanding Moscow ally Moamer Kadhafi, which Moscow allowed to go ahead by abstaining at the Security Council.

With Putin now back as president after a four-year stint as prime minister, Russian foreign policy has become newly assertive, notably avoiding further diplomatic irrelevance by abstaining at the United Nations.

Russia also has military and political interests in Syria dating back to the Soviet Union’s alliance with Assad’s father and predecessor Hafez al-Assad that it is not willing to surrender in a hurry.