The war-time leader has been a central figure at recent summits but given his fractious relationship with Trump, Zelensky has not been invited to the main working session with NATO members.

"The teams are finalising the details" of the meeting, the source told AFP, adding that the talks were scheduled for the "early afternoon" in the Netherlands.

The source added that the discussion would focus on Ukraine's "purchase of a defence package, a large part of which consists of air defence systems".

The leaders would also discuss more "sanctions against Russia, and a price cap on oil", the source added.

Ukraine and its allies have sought to lower an existing oil cap imposed on Russia after it invaded Ukraine more than three years ago, from $60 to $45, to dent the Kremlin war chest.

Trump so far has frustrated Western allies by refusing to impose new sanctions on Russia despite President Vladimir Putin's refusal to agree to a Ukraine ceasefire.