Jeremy Corbyn has called for Western leaders to "de-militarise" the border between Russia and Eastern Europe or risk a new cold war.
The Labour leader said he had some criticisms of Vladimir Putin, but that the West had to ensure it did not pile up forces on Russia’s border.
It comes after Nato, which Mr Corbyn has been a long-term critic of, announced a new deployment in Eastern Europe and put troops on high alert amid rising tension with Moscow.
Speaking to BBC presenter Andrew Marr , Mr Corbyn said: "I have many, many criticisms of Putin, of the human rights abuses in Russia, of the militarisation of society.
"But I do think there has to be a process that we try de-militarise the border between what are now the Nato states and Russia, so that we drive apart those forces and keep them further apart in order to bring about some kind of accommodation.
"We can’t descend into a new cold war. "
A week ago some 300,000 Nato troops were been put on alert amid rising tensions between Russia and the Baltic states.
Jens Stoltenberg, the secretary-general of Nato, said the alliance hoped to speed up the response time of thousands of its troops to allow it to more rapidly react to threats.
Nato revealed in October it is preparing to station 4,000 troops on the Russian border with the Baltic states in its biggest military build-up since the Cold War. The troops will be summoned from nations across the alliance, including the UK.
Mr Corbyn suggested in his interview that the Organisation for Security and Co-operation in Europe, which includes Russia, could replace Nato as a forum for solving issues in the region.
During the Leadership contest Mr Corbyn stoked controversy after refusing to directly back upholding Nato's article five, which commits countries to defend each other if attacked.
