Britain ordered 1,000 troops to be on a state of readiness to provide support in the event of a humanitarian crisis caused by any Russian aggression, ahead of a visit by Prime Minister Boris Johnson to the leaders of NATO and Poland on Thursday.
Johnson will go to Brussels and Warsaw to stress the need to hold firm on NATO's principles and discuss ways that Britain can provide military support while Russia amasses its troops near Ukraine's border.
Johnson's trip is one among a wave of international diplomatic efforts. French President Emmanuel Macron met Russian President Vladimir Putin earlier this week, and U.S. Vice President Kamala Harris is due to have in-person meetings with U.S. allies and partners at the Munich Security Conference next week.
Britain's foreign secretary and defense secretary are also due in Moscow this week for talks with their counterparts.
"The U.K. remains unwavering in our commitment to European security," Johnson said in a statement. "As an alliance, we must draw lines in the snow and be clear there are principles upon which we will not compromise."
Britain said on Monday that it would send a further 350 troops to Poland, after it sent 100 troops last year to help with a migrant crisis at its border with Belarus.
Johnson's office repeated on Wednesday that any further military incursion of Ukraine by Russia would likely create the mass forced displacement of people on Europe's border, affecting countries like Poland and Lithuania. In 2014, Russia annexed the Crimean Peninsula from Ukraine.
Johnson's office said the prime minister would also discuss with NATO's Jens Stoltenberg the U.K.'s offer to bolster the alliance's defenses, including a doubling of troops in Estonia, more RAF jets in southern Europe, and the sailing of both the Trent patrol vessel and a Type 45 destroyer to the Eastern Mediterranean.