Ukrainian President Volodymyr Zelensky is joining European leaders in talks aimed at increasing pressure on US President Donald Trump to side with Ukraine during Friday's summit with his Russian counterpart in Alaska, BBC reported.

In an online call with Trump on Wednesday, the leaders are expected to reiterate that no decisions should be taken without Ukraine, including changing its borders by force.

Trump has said any peace deal would involve "some swapping of territories" and it is believed one of Russian President Vladimir Putin's demands is that Kyiv surrenders the parts of the Donbas it still controls.

On Tuesday, Zelensky said such a concession could be used as a springboard for future attacks by Russia, which has been making gains recently, according to BBC.