Boris Johnson, 57, is set to hold a COBRA meeting, a Number 10 spokesman has confirmed.
The announcement comes after Russian President Vladimir Putin, 69, said Moscow would recognise two regions in east Ukraine as independent states.
The Number 10 spokesman said: “The Prime Minister will chair a COBRA at 6.30am to discuss the latest developments in Ukraine and to coordinate the UK response including agreeing a significant package of sanctions to be introduced immediately.”
Reports also indicate Mr Johnson is considering sending further defensive support to Kiev.
Ukrainian President Volodymyr Zelenskyy, 44, also revealed he had spoken to Mr Johnson about the developments.
Mr Zelenskyy said on Twitter: “After the meeting #РНБО discussed the current situation with BorisJohnson.
“We are currently preparing an appeal as soon as possible, and then talks with European Commission President and Recep Tayyip Erdogan are planned.”
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