Ukrainian President Volodymyr Zelensky believes Russia is preparing to "wage war" against a weakened NATO should President Donald Trump dilute US support for the alliance.

In an interview with broadcaster NBC on the sidelines of the Munich Security Conference, Zelensky also said Trump had the leverage to push Vladimir Putin into ceasefire negotiations over Ukraine, but warned the Russian leader should never be trusted.

"We believe that Putin will wage war against NATO," Zelensky told the network in an interview aired Sunday. 

He suggested Putin may be waiting "for a weakening of NATO," which could be triggered by the possibility "that the United States of America will think to take its military from Europe."

An emboldened Russia would move swiftly into territorial expansionist mode, the Ukranian leader said.

"I don't know (if) they will want 30 percent of Europe, 50 percent, I don't know. Nobody knows. But they will have this possibility," he said. 

Zelensky's comments to NBC echoed his remarks to the Munich conference on Saturday, where he urged the creation of a European army, arguing the continent could no longer count on Washington.

"We can't rule out the possibility that America might say no to Europe on issues that threaten it," Zelensky told the conference.  

"I really believe that time has come. The Armed Forces of Europe must be created."

The push for a joint continental force has been mooted for years without gaining traction and Zelensky's intervention seems unlikely to shift the balance.

'A little bit scared'

Zelensky's latest warnings came as Washington announced a team of senior US officials would meet in Saudi Arabia with counterparts from Moscow and Kyiv. 

Trump upended the status quo this week when he announced he was likely to soon meet Putin to start talks to end the conflict.

Zelensky said that in conversations with Trump, the president indicated he believed Putin was for ready for negotiations. 

"I said to (Trump), 'No, (Putin)'s a liar. He doesn't want any peace.'"

But Zelensky added that he thinks Putin is "a little bit scared" of the US president.

"I think that really he can push Putin to peace negotiations," Zelensky said, adding, "Don't trust him. Don't trust Putin."

US officials have sought to assure Ukraine that it will not be left in the cold after three years of battling Russia's invasion. 

After sitting down with Zelensky in Munich, US Vice President JD Vance said the United States was looking for a "durable, lasting peace" that would not lead to further bloodshed in coming years.

But Washington has sent mixed messages to Kyiv, with Pentagon chief Pete Hegseth appearing to rule out Ukraine joining NATO or retaking all of its territory.