"The Prime Minister was clear that our support for Ukraine is unwavering - international borders must not be changed by force and Ukraine must have robust and credible security guarantees to defend its territorial integrity as part of any deal," a readout of a call from Starmer's Downing Street office said.

Ukrainian President Volodymyr Zelenskyy said Tuesday that it is "impossible to talk about Ukraine without Ukraine" ahead of the upcoming meeting between Russian President Vladimir Putin and U.S.