The first of 800 UK troops being sent to bolster Nato defenses in the Baltic have arrived in Estonia. The 120 soldiers from the 5th Battalion the Rifles will set up a UK headquarters in the country before the remaining troops arrive in April.
The defense secretary said they would deter "Russian aggression". The UK is taking a leading role in Nato's "enhanced forward presence" operation, aimed at reinforcing the alliance's eastern border.
Defense Secretary Sir Michael Fallon told the BBC it was the biggest UK military deployment in Europe since the end of the Cold War and formed part of a long-term, open-ended commitment to deter Russia.
He said deploying troops was necessary "because of the increased Russian aggression that we've seen and the need to reassure our allies on the eastern side of Nato". But Sir Michael insisted it was a "defensive deployment" and was not "designed to provoke or escalate".
BBC defence correspondent Jonathan Beale said the troops say they are well prepared for a range of threats, and the UK government is aware that Russia might use misinformation, fake news and other provocations during their deployment.
The first waves of soldiers flew from RAF Brize Norton, in Oxfordshire, on Friday, and were met at Amari air base in Estonia by the country's defense minister, Margus Tsahkna.