British troops are to be deployed to the Baltics as part of a long-term Nato mission to deter Russian aggression.
Defence Secretary Michael Fallon said a "small number" of soldiers would be stationed there to "watch over our allies on the eastern borders".
RAF Typhoon fighters are already in the region as part of the Baltic Air Policing detachment and have been called into action in recent months.
The Syrian conflict will not become a "proxy war" between the United States and Russia, President Obama has said.
Mr Obama said he wanted Russia to be successful and help deal with global problems, but its approach to Syria was not a "smart strategic move".
"This is not a contest between the United States and Russia," the US President told a press conference on Friday.
"We're not going to make Syria into a proxy war between the United States and Russia. That would be bad strategy on our part.
"This is not some superpower chessboard contest."
Incursions by Russian jets into Turkish airspace have prompted a stern response from Nato's most powerful ally.
Here's what you need to know about this latest development in the increasingly bloody, complicated and volatile conflict.
Russia urges world leaders to unite to fight terrorism in Syria amid criticism that air strikes have targetted rebel fighters and civilians.