The presidents of Poland, Lithuania, Latvia and Estonia are on their way to Kyiv to meet Ukraine's President Volodymyr Zelenskiy, an adviser to the Polish leader said on Wednesday.

The four join a growing number of European politicians to visit the Ukrainian capital since Russian forces were driven away from the country's north earlier this month.

"Heading to Kyiv with a strong message of political support and military assistance," Lithuanian President Gitanas Nauseda tweeted on Wednesday, along with a picture of the presidents next to a train.

The "symbolic" visit will include talks about the details of support, Pawel Szrot, head of the Polish president Andrzej Duda's office told private broadcaster Polsat News.

It comes the day after U.S. President Joe Biden said Moscow's invasion of Ukraine amounted to genocide, while President Vladimir Putin promised Russia would "rhythmically and calmly" continue its operation and achieve its goals.

The four presidents' offices declined to provide details of the visit for security reasons.

Putin sent his troops into Ukraine on Feb. 24 on what he calls a "special military operation" to demilitarise and "denazify" Ukraine. Ukraine and the West say Putin launched an unprovoked war of aggression.

German President Frank-Walter Steinmeier planned to visit Kyiv at the same time "to send a strong signal of European solidarity with Ukraine there," but was not welcomed by Ukraine, he said on Tuesday.

German Bild newspaper reported that Zelenskiy had rejected Steinmeier's plans to visit due to his close relations with Russia in recent years and his support for the Nord Stream 2 gas pipeline designed to double the flow of Russian gas to Germany, which has since been suspended.

(Reporting by Pawel Florkiewicz in Warsaw and Andrius Sytas in Vilnius; Editing by Clarence Fernandez and Tomasz Janowski)