The Ukrainian president also said plans for NATO members to increase defence spending to 5% of GDP by 2035 are "very slow".

The Ukrainian president said Russian President Vladimir Putin could attack a NATO country within five years to test the alliance.

The group has truncated its summit to focus on a 5% per-country spending target, something Trump supports, to avoid upsetting him.

The NATO alliance has crafted a summit in The Hague this week to shore itself up by satisfying U.S. President Donald Trump with a big new defence spending goal - but it now risks being dominated by the repercussions of his military strikes on Iran.

President Donald Trump’s first appearance at NATO since returning to the White House was supposed to center on how the U.S. secured a historic military spending pledge from others in the alliance

NATO leaders meeting this week in The Hague will confront the prospect of another open-ended U.S.-led war outside the North Atlantic region the alliance was created to defend.