Russia is deliberately attacking civilians in northern Syria in an attempt to intensify the refugee crisis, western diplomats and politicians have warned, in a sign that a fragile ceasefire agreement for the war-ravaged country is crumbling before it begins.

A pivotal part of Russia's strategy was "to exacerbate the refugee crisis and use it as a weapon to divide the transatlantic alliance and undermine the European project", US Senator John McCain said in a speech at an annual security conference in Munich on Sunday. Two senior politicians from close US allies and a senior European intelligence official echoed Mr McCain's remarks, reflecting the bleak mood among western defence chiefs, diplomats and political leaders gathered for the conference.

Moscow was "weaponizing" the refugee crisis for leverage, one of the politicians warned. According to a European official, facilities such as bakeries and hospitals were being hit in an attempt to force the local population into capitulation and increase the flow of refugees towards Turkey and Europe.

The Syrian ceasefire deal, which is set to begin on Friday, was agreed by the International Syria Support Group — the collection of regional and world powers whose influence is critical in determining the outcome of the Syrian conflict — on the eve of the conference last Friday. Moscow's air operations have shifted the balance of power in favour of the regime of Bashar al-Assad, leaving many Washington-backed moderate opposition groups in northern Syria close to surrendering. "This is diplomacy in service of military aggression, and it's working because we are letting it," said Mr McCain. "It is no accident that Mr Putin has agreed on a cessation of activities when he did. We have seen this movie before in Ukraine," he added. More from the Financial Times:

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Mr McCain, chairman of the US Senate armed services committee, gave public voice to widespread concerns over the ISSG deal that have been simmering among some of Washington's closest allies. Though the agreement has been cautiously welcomed in public, in private most do not think it will succeed. The Russian bombing of Aleppo — Syria's largest city, which is now almost completely encircled by Mr Assad's ground forces — has continued over the course of the weekend, in spite of the ISSG pledge to begin an immediate rollback of military activities. The attacks are rapidly worsening the plight of civilians in the city, according to local observers and humanitarian agencies.

Sen. John McCain Getty Images