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.
Russia has reportedly carried out its first air strikes in Syria, a US official has told Reuters.
It comes just hours after Russian Parliament gave Vladimir Putin approval to use military force against so-called Islamic State in Syria.
According to the official, who was speaking on condition of anonymity, the military action was carried out in the vicinity of the city of Homs and American forces were given prior notice of the intended attack.
Footage posted on YouTube claimed to show Russian jets flying in the sky above Syria today:
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.