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.
A Russian warplane violated Turkey's airspace for a second time on Sunday, said the Turkish Foreign Ministry.
The ministry summoned the Russian ambassador late on Monday to protest against the violation.
Turkish jets were scrambled after a Russian warplane violated Turkey's air space on Saturday but Russia blamed a "navigational error".
The Cold War adversaries believe in different solutions to end Syria's civil war.
Turkey's belief is that Syrian President Bashar al-Assad has to go for the conflict to end whereas Russia backs the Syrian leader. Turkey, a Nato member, has called the Russian strikes a "grave mistake".
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.