The British and US defence ministers are warning of a "persistent pattern of interference" in other nations by Russia, saying it is acting as a "strategic competitor" to the West.
British Defence Secretary Michael Fallon said on Friday there could be no return to "business as usual" with Russia because of its "interference in different parts of the globe."
Following talks in London with US Secretary of Defence Jim Mattis, Fallon said his government is working with Russia to "deconflict" in Syria and in areas where Russian planes fly close to British air space.
"And we engage with Russia about parts of the world where Russia has great influence, but otherwise we need to be extremely watchful now of this persistent pattern of Russian interference," he said at a joint press conference.
Mattis, a veteran of wars in the Gulf, Afghanistan and Iraq, accused Russia of "mucking around" in other countries' elections.
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He was "concerned" about reported links between Russia and the Taliban in Afghanistan, he said without elaborating.
"We look to engaging with Russia on a political or diplomatic level but right now, Russia is choosing to be a strategic competitor and we're finding that we can only have very modest expectations of the areas where we can cooperate," Mattis said.
"It's no longer a cooperative engagement with them."
Fallon said Britain's deployment of additional troops to Estonia and Poland is a response to "Russian aggression" in the region.
"This is part of the biggest [British] deployment in eastern Europe since the Cold War," he said.
