UK troops heading to Baltic states following Russia's intervention in Syria
Britain is to station troops in the Baltic states amid growing tension with Russia in the wake of President Vladimir Putin's military intervention in Syria.
Defence Secretary Michael Fallon said the deployment of a company size detachment - numbering around 100 personnel - was part of a "more persistent presence" by Nato forces in eastern Europe.
"This is further reassurance for our allies on the eastern flank of Nato - for the Baltic states and for Poland," he said, as he arrived in Brussels for a meeting of alliance defence ministers.
"That is part of our more persistent presence on the eastern side of Nato to respond to any further provocation and aggression."
The troops, who are expected to be deployed in the coming months, will form part of a US/German-led training, evaluation and capacity-building mission in Poland and the Baltic states of Latvia, Lithuania and Estonia.
The move came as Nato secretary general Jens Stoltenberg announced plans had been finalised for a new response force of up to 40,000 - twice the current size - and new Nato headquarters offices in Hungary and Slovakia.
"All of this sends a clear message to all Nato citizens. Nato will defend you, Nato is on the ground, Nato is ready," he said.
Mr Stoltenberg condemned the latest escalation in Syria, which saw Russian warships in the Caspian Sea launch cruise missile strikes against opposition forces fighting President Bashar Assad.
He also strongly denounced the "unacceptable" violations of Turkish airspace by Russian war planes conducting air strikes against the rebels.
"The Russian actions and the support to the regime are not helpful," he said. "We stand in strong solidarity with Turkey."
His comments were echoed by Mr Fallon who said Russia's intervention was making "a very serious situation in Syria much more dangerous".
"If Russia wants to help here, the single most helpful thing they can do is use their influence on Assad to stop barrel-bombing his own civilians, their children, his own cities and villages. That's how Russia could help to resolve this conflict," he said.
There was no sign, however, Russia was preparing to draw back, as Syria's chief-of-staff said Moscow's support had enabled the regime forces to mount a wide-ranging ground offensive against the rebels.
In a rare televised address, General Ali Ayoub said the Russian strikes had facilitated an expanded military operation to eliminate "terrorists" - a term the Syrian government uses to refer to all armed opposition to the regime.
The Russians insist they are targeting Islamic State (IS) extremists - also referred to as Isil or Isis - but Western sources say they have largely hit mainstream opposition forces.
They believe the air strikes are primarily designed to prop up Assad, who Britain, the US and other Western countries insist must go as part of any political settlement of Syria's four-year civil war.
Former MI6 chief Sir John Sawers said there was now a "real danger" of a clash between the Russians and the US and its coalition partners who are attacking IS in eastern Syria.
"It is going to be quite hard to continue this campaign unless there is a degree of military co-ordination between the Russians and the West," he told the BBC Radio 4 Today programme.
"You can't really have two air forces fighting different campaigns aimed at different objectives over the same territory without the real risk of a clash."