LONDON: British Prime Minister Boris Johnson will on Thursday preside over an emergency meeting to discuss the "horrific" Russian attack on Ukraine, his office said.

"The prime minister will chair a COBR at 0730 (local and GMT) to discuss the response to the horrific attacks in Ukraine this morning," a Downing Street spokesperson said.

Johnson earlier spoke to Ukrainian President Volodymyr Zelensky and said "the West would not stand by as President (Vladimir) Putin waged his campaign against the Ukrainian people," his office said.

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"President Putin has chosen a path of bloodshed and destruction by launching this unprovoked attack on Ukraine.

The UK and our allies will respond decisively," Johnson added in a tweet.

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Putin early Thursday launched an air and ground assault on Ukraine after a surprise television address.