Britain expects US President-elect Donald Trump to "stand up" to Moscow as Russia tests Western resolve, Defence Secretary Sir Michael Fallon has said.
Sir Michael insisted that Britain was not in danger of becoming internationally isolated by its tough stance towards Vladimir Putin after Mr Trump expressed admiration for the Russian president during his bid for the White House.
He told BBC Radio Four's Today programme: "I think you have to distinguish between the campaign rhetoric of President-elect Trump and what he does in practice. In practice, every American administration has always stood up to Russia.
"We are not suggesting you shouldn't talk to Russia, but what you can't do is treat Russia as business as usual, as any kind of equal partner."
Asked if he had any contact with the president-elect's team, Sir Michael said: "Our people are talking to people who are advising Trump, and we are waiting for his nomination of defence secretary."
Sir Michael warned that Mr Putin was trying to test the Western alliance, and countries on Nato's eastern flank needed reassurance.
He said: "'Test' is the right word, that is what he has been doing.
"We have seen long range aviation, Russian bombers flying down the edge of our flight region, we have seen more submarine activity, we have seen manoeuvres on the borders outside the Baltic States, and across the border from Poland, we have seen more maritime activity in the Baltic, we have had this carrier group sail through the English Channel. So, Putin, I think, is testing the alliance and we have to respond.
"We have to make clear that Nato is a defensive alliance, but equally it is prepared to come to the defence of those members who feel very vulnerable, particularly on the eastern flank."
Mr Trump sparked alarm in Nato during his campaign when he suggested the US may not fulfil its collective defence obligations if the Baltic States were attacked unless they increased their military spending.
The UK is to deploy around 150 troops from the Light Dragoons regiment in Catterick, along with a number of armoured vehicles, to Orzysz in north-east Poland, close to the border with the Russian enclave Kaliningrad, next year in a bid to underline London's commitment to Nato's collective defence agreement.