Former Soviet Premier Mikhail Gorbachev has accused Nato of preparing for "offensive operations" against Russia.
As the Western alliance held a summit in Warsaw, Poland, Mr Gorbachev criticised Nato’s decision to deploy 4,000 more international troops in Eastern Europe.
Tensions have been mounting between Russia and Nato member states, in particular the US, as diplomatic spats and military excercises have increased in frequency.
Mr Gorbachev, the eighth and last leader of the Soviet Union, said: “Nato has begun preparations for escalating from the Cold War into a hot one.
“All the rhetoric in Warsaw just yells of a desire almost to declare war on Russia. They only talk about defence, but actually they are preparing for offensive operations.”
However, Nato’s Secretary-General Jens Stoltenberg said the organisation’s decision to triple its military presence in Eastern Europe was a purely defensive move.
“Nato poses no threat to any country. We do not want a new Cold War. We do not want a new arms race. And we do not seek confrontation," he said.
The move comes after concerns among Western countries regarding the intentions of President Vladimir Putin after Russia's annexation of Crimea from Ukraine in 2014.
Prior to the Nato summit, Russia assembled troops, trucks and equipment at its Baltic bases, highlighting its military readiness.
In a speech after Nato leaders agreed to increase troop numbers in eastern Europe, Mr Stoltenberg said: “What we have seen is a Russia which has invested heavily in modern defence capabilities over many years, which has modernised its forces, its equipment, and has used military force against a sovereign nation in Europe, violating Ukraine’s territorial integrity and sovereignty, and that's the reason why we have increased our presence in the eastern part of the alliance.
“Russia is neither a strategic partner – we are not in the strategic partnership with Russia which we tried to develop – but we are neither in a Cold War situation.
“We are in a new situation which is different to anything else we have experienced before.”
As part of the reinforcement, Britain will send a 500-strong battalion to Estonia and a further 50 troops to be stationed in Poland.
Canada will send a battalion to Estonia’s Baltic neighbour, Latvia, and US President Barack Obama announced on his arrival in Warsaw that the United States would deploy 1,000 troops to Poland “to serve shoulder to shoulder with Polish soldiers”.
Meanwhile, ‘tit-for-tat’ diplomatic expulsions between Russia and the US have continued. On Saturday, Russia expelled two American diplomats it claims were working undercover for the CIA.
"After their unfriendly step two employees of the US Embassy had to leave Moscow," Deputy Foreign Minister Sergei Ryabkov said in a statement.
The move is seen as retaliation for the US expulsion of two Russians, which came in the wake of a scuffle between a Russian policeman and an American diplomat outside the U.S. embassy in Moscow in June.
Mr Ryabkov continued: "They were declared persona non grata for activities incompatible with their diplomatic status."
"We hope Washington recognises all the same the perversity of its anti-Russian line. If they decide there to move further along the path of escalation it will not remain unanswered."
Russia claimed the American tried to rush into the embassy late at night after a spying mission, without presenting identification, and was tackled by the policeman. But footage purporting to be of the incident, broadcast on Russian television, showed the policeman burst through a door and tackle a man without warning.
The diplomat involved is one of the two Americans expelled, Mr Ryabkov said on Saturday.
US officials serving in Russia have also reported suffering harassment from Russian security services.
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