LATEST: UK ready to support Ukraine over threat from Russia says Theresa May
Theresa May vowed to support Ukraine in the face of the "threat" from Moscow as she welcomes Petro Poroshenko to Downing Street.
She told the Ukrainian president the UK stood "ready to support" his country.
Mrs May said she would continue to press for sanctions to remain in place against Russia until the Minsk agreement on a political settlement was fully implemented.
She said: "We recognise of course the threat from Russia not only seen in the annexation of Crimea but also in activity in eastern Ukraine.
"We continue to stand ready to support you against this threat, both through our bilateral security and defence co-operation but also in other ways.
"We will continue to press for sanctions to remain until the whole Minsk agreement is fully implemented."
The International Court of Justice has rejected Ukraine's request for measures aimed at blocking Russian support for rebels in the east of the country.
But the court imposed measures to rein in discrimination by Moscow against ethnic Tatars and other minorities in Crimea.
The UN court also said that it expects both Moscow and Kiev to work to implement the Minsk agreements that were designed to bring peace to conflict-ravaged eastern Ukraine.
At hearings last month, Ukraine accused Russia of sponsoring terrorism by providing funds and weapons to rebels in Ukraine and of discriminating against Tatars and others in Crimea.
Lawyers for Russia rejected the allegations.
Wednesday's ruling was preliminary decision aimed at preserving Ukraine's rights while the full case makes its way through the court, a process likely to take years.
