Russia says it is pulling back some of its troops from near Ukraine after a build-up raised fears of an invasion. The defence ministry said that large-scale drills continued but that some units were returning to their bases.  There has been no independent confirmation of the withdrawal and international powers have reacted cautiously to the announcement.  More than 100,000 Russian troops have massed at Ukraine's border. Russia has always denied it is planning an attack. Russia has deep cultural and historic ties with Ukraine, and has been seeking guarantees it will not join the Nato military alliance, something the bloc has refused to promise.  Troops began gathering in large numbers last November, bring increasingly dire warnings about Russia's intentions. In recent days the US warned an invasion could be imminent, and moved its embassy out of the capital Kyiv.   Nato said the Russian announcement gave cause for "cautious optimism" but that they had not seen evidence of de-escalation on the ground. In its statement, Russia's defence ministry said it was withdrawing some of the troops conducting exercises in military districts bordering Ukraine.  "A number of combat training exercises, including drills, have been conducted as planned," defence ministry spokesman Igor Konashenkov said. Some exercises are continuing, such as a large joint Russia-Belarus drill, due to end on 20 February. A British government source said it was waiting to see the scale of the withdrawal, saying it would have to make a difference to the ability to invade to be meaningful. But the announcement was enough for both Ukraine and Russia to claim victory in the stand-off. Ukraine's Foreign Minister Dymytro Kuleba said he would believe the withdrawal when he sees it but "we have managed together with our partners to deter Russia from any further escalation".  A Russian foreign ministry spokeswoman, Maria Zakharova, said the day "will go into history as the day western war propaganda failed. They have been disgraced and destroyed without a single shot being fired."