Kallas also emphasized that if an agreement is reached between the US and Russia on the Ukrainian issue, it must take place with the participation of Ukraine and the EU.

"[US] President Donald Trump is right that Russia must end the war against Ukraine. The US has the power to force Russia to engage in serious negotiations. Any deal between the US and Russia must include Ukraine and the EU, because this is a matter of security for Ukraine and the whole of Europe," Kallas said in a statement.

"I am calling an emergency meeting of EU foreign ministers on Monday to discuss our next steps," Kallas said. The meeting will be held online.

"We are working to achieve a sustainable and just peace, and international law clearly states that all temporarily occupied territories belong to Ukraine," the EU foreign policy chief stressed.

She also warned that any agreement"must not become a stepping stone for further Russian aggression against Ukraine, the transatlantic alliance and Europe."

It has already been reported that a meeting between US President Donald Trump and Russian dictator Vladimir Putin is scheduled for Friday in Alaska, where options for ending hostilities in Ukraine will be discussed.

Trump has said that an agreement between Russia and Ukraine would mean"there will be some exchange of territory," without providing further details.

But Ukrainian President Volodymyr Zelensky has already rejected any proposals that would threaten Ukraine's territorial integrity, saying that Kiev"will not give Russia any rewards for what it has done" and that "Ukrainians will not give their land to the occupier."

The Ukrainian Constitution prohibits the surrender of territory.

The leaders of Britain, France, Italy, Germany, Poland and Finland, as well as European Commission President Ursula von der Leyen, issued a statement on Sunday, stressing that"the path to peace in Ukraine cannot be determined without Ukraine."