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.
Reports of civilian deaths resulting from Russian air strikes in Syria emerged before the country's jets left the ground, President Vladimir Putin has claimed.
President Putin said Russian and US special services were developing contacts to exchange information on what they were doing in Syria.
He told a meeting of the Russian Council for Civil Society and Human Rights that the move should prevent inaccurate "information attacks" about what his forces were doing in the country.
"As for any information in the media on civilians suffering [from Russian airstrikes], we were ready for such information attacks," President Putin said.
"I draw your attention to the fact that the first reports on civilian casualties emerged before our planes even left the ground."
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.