Britain is to station a "small number" of troops in the Baltic states in a further move to deter Russian aggression, Defence Secretary Michael Fallon has said.
Arriving for a meeting of Nato defence ministers in Brussels, Mr Fallon said the deployment was intended to reassure former Soviet bloc members of the alliance.
"This is further reassurance for our allies on the eastern flank of Nato - for the Baltic states and for Poland," he said.
"That is part of our more persistent presence on the eastern side of Nato to respond to any further provocation and aggression."
Mr Fallon said the British troops would be part of a new Nato training, evaluation and capacity-building mission in Poland and the Baltic states of Latvia, Lithuania and Estonia.
"They will be part of a more persistent presence by Nato forces," he said.
The move comes against a backdrop of heightened tension between the West and Moscow, following President Vladimir Putin's decision to launch air strikes in Syria.
The Russians insist they are targeting Islamic State (IS) extremists - also referred to as Isil - but Western powers say they have largely hit mainstream opposition forces.
The West believes the air strikes are primarily designed to prop up the regime of President Bashar Assad, who Western countries insist must go as part of any political settlement of Syria's four-year civil war.
"Russia is making a very serious situation in Syria much more dangerous," Mr Fallon said.
"We will be calling on Russia specifically to stop propping up the Assad regime, to use their influence constructively to stop Assad bombing his own civilians and themselves to avoid the use of unguided munitions in areas that are not being controlled by Isil," Mr Fallon said.
"If Russia wants to help here, the single most helpful thing they can do is use their influence on Assad to stop barrel-bombing his own civilians, their children, his own cities and villages. That's how Russia could help to resolve this conflict."
RAF Typhoon fighters are already deployed in eastern Europe as part of the Baltic Air Policing detachment and have been called into action in recent months.
In June, Typhoons were scrambled from Amari Air base in Estonia to intercept and shadow two Russian military aircraft over the Baltic Sea.