He spoke as vital US aid to Ukraine has been blocked by the US Congress and as Russia has been emboldened by fresh gains in recent weeks.

"The most important thing is to unblock the sky. Air defence and future jets will help it," Zelensky told reporters at a press conference in the western city of Lviv.

"What's important is that all our decisions have to come in time. I think that is the priority," he said, adding that Ukraine had seen delays to promised shipments during last year's failed counter-offensive.

He said air defence was critical to saving civilian lives and "strengthening of our army on the frontline".

Zelensky was speaking alongside Danish Prime Minister Mette Frederiksen, as Western leaders descend on the country in a show of support for Kyiv as the war enters its third year.

NATO member Denmark has promised to deliver F-16 fighter jets to Ukraine later this year, and Several NATO countries have been training Ukrainian pilots on the advanced planes for months.

Ukraine relies on Western military backing to help it defend against Russian attacks, which have accelerated as Moscow seeks to take advantage of Kyiv's stretched resources on the battlefield.

A vital $60 billion military aid package for Ukraine from Washington is currently held up in the US Congress amid domestic political wrangling.