United States President Donald Trump has called for Russia and Ukraine to freeze the war along current battle lines – a proposal that would see Moscow keep large areas of Ukrainian territory.

Trump told reporters late on Sunday that the two sides should just stop fighting and resolve the "details" over territory at future talks. The current front line runs through the Donbas region, an industrial hub.

"What I say is they should stop right now at the battle lines, go home, stop killing people and be done," the US president said, adding that it would be difficult to negotiate details of a final resolution.

Asked about what would happen to Donbas, which has seen most of the fighting, Trump said: "Let it be cut the way it is. It's cut up right now – I think 78 percent of the land is already taken by Russia. You leave it the way it is right now. They can negotiate something later on down the line."

Ukraine has previously insisted on reclaiming all of its land. Trump himself asserted last month that Ukraine can win militarily and recapture all of the territories occupied by Russia, which also includes the Crimean Peninsula and other areas in eastern Ukraine, reports Al Jazeera online.

The US president, who had promised to swiftly end the war between Russia and Ukraine, is set to meet his Russian counterpart, Vladimir Putin, in Hungary in the coming weeks.

Zelensky has said he would be ready to join Putin and Trump at their summit in Hungary if he is invited.

Meanwhile, Ukraine is preparing a contract to buy 25 Patriot air defence systems, Volodymyr Zelensky said, in what would be a huge boost to Kyiv's abilities to defend against Russia's aerial bombardments.

In comments to media at a meeting on Sunday and cleared for use yesterday, Zelensky said the systems would be supplied every year for a number of years, and that Ukraine would seek for some European nations to give Kyiv priority in the queue for the systems.

Patriots are seen by Kyiv as the most effective systems to stop Russian ballistic missiles, which travel several times faster than the speed of sound, reports Reuters.