President Donald Trump said Monday the announcement by his Russian counterpart Vladimir Putin of a nuclear-powered cruise missile test was not "appropriate."

"He ought to get the war (in Ukraine) ended. A war that should have taken one week is now soon in its fourth year. That's what he ought to do instead of testing missiles," Trump told journalists aboard Air Force One.

Putin on Sunday announced the successful final test of the Burevestnik missile, which he said has "unlimited range."

Trump had promised to quickly end the Ukraine war upon his return to the White House in January, but talks between Moscow and Kyiv have stalled despite the president's mediation efforts.

Russia's forces are slowly but steadily gaining ground in Ukraine, grinding through Kyiv's defenses in costly battles.

Trump last week slapped sanctions on Russia's two largest oil companies, complaining that his talks with Vladimir Putin to end the Ukraine war have yet to yield results.

"Every time I speak with Vladimir, I have good conversations, and then they don't go anywhere," the president lamented.