British Prime Minister Boris Johnson warned Russian President Vladimir Putin in a call on Monday that any destabilising action against Ukraine would be a strategic mistake with significant consequences, Downing Street said.

“The Prime Minister emphasised the UK’s commitment to Ukraine’s territorial integrity and sovereignty, and warned that any destabilising action would be a strategic mistake that would have significant consequences,” a spokesman said.

“He expressed the United Kingdom’s deep concern over the build-up of Russian forces on Ukraine’s border, and reiterated the importance of working through diplomatic channels to deescalate tensions and identify durable solutions.”