BRITAIN will send hundreds more troops to deploy on Russia's border, as the Prime Minister said the West also had to "put pressure" on Moscow over the Syria crisis.
Around 800 soldiers - along with tanks, armoured vehicles and drones - will now head to Estonia in the spring in a Nato effort to reassure the Baltic states over Russian aggression.
The boosted deployment, up from 500 announced earlier this year, will be Britain's largest long-term -deployment to one of Russia's neighbours since the end of the Cold War.
Defence sources said the six-month deployment to Tapa army base, around 100 miles from the border, was the start of a persistent British presence.
The British troops will form one of four Nato battalions being deployed in response to a perceived threat from Russia to the alliance's eastern allies.
The announcement came as Russia abandoned plans to refuel and provision warships headed for the war in Syria at a Spanish port following international pressure on Madrid.
Russia's embassy in Spain said on Wednesday that vessels from a squadron led by the Admiral Kuznetsov, -Russia's only aircraft carrier, would not stop as planned for refuelling in Ceuta, a Spanish port in North Africa.
Eight ships from Russia's northern fleet, including the Admiral Kuznetsov and the Peter the Great, a missile--carrying battle cruiser, passed through the English Channel en route to Syria last week.
The group is expected to join a flotilla operating off the coast of Syria, where the Kuznetsov's planes may be used in bombing raids over Aleppo.
Theresa May said: "What we have seen, sadly, is that the Russians are -already able to unleash attacks on innocent civilians in Syria. What matters is that we put pressure on Russia to do what everybody agrees is the only way that we are going to resolve this issue, which is to ensure that we have a political transition in Syria, and that's where we should focus our attention."
Defence -Secretary Sir Michael Fallon said the battle to liberate the Syrian city of Raqqa, the capital of -IS's so-called caliphate, will begin within weeks.
Meanwhile, concerns were growing about the apparent deployment of two powerful Russian missile corvettes to the Baltic. Both carry long-range -nuclear-capable Kalibr cruise missiles, and will join Russia's Baltic fleet in -Kaliningrad, Izvestia, a pro-government broadsheet, reported.