British Prime Minister Boris Johnson on Monday said the UK has "significant concerns" over Russian activity in the Crimea and on the Ukrainian border. "The Prime Minister, during a phone call to Ukraine President Volodymyr Zelensky, reaffirmed his "unwavering support for Ukraine's sovereignty and territorial integrity," Johnson's office said in a statement. He expressed his solidarity with President Zelensky's government "in the face of this destabilising activity and commended Ukraine's approach to the situation," it added. csp/pvh