Making a virtual appearance at a summit of European leaders in Sofia, Biden expressed his country's strong support for the initiative, according to officials.
The Polish-led Three Seas Initiative aims to boost infrastructure, energy and business ties among 12 countries between the Black, Baltic and Adriatic Seas.
“There is incredible potential for increasing cooperation and connectivity among this group," Biden told the Three Seas Summit and Business Forum on Thursday.
"That will enhance the security and prosperity of the region, and, quite frankly, benefit the world," he added.
"The United States will be your unfailing partner at every step," he also said.
The US Department of State said in a tweet that the United States "wholeheartedly supports the Three Seas Initiative and its goal of a stronger, united, and more competitive Europe."
It added that "increasing connectivity and cooperation benefits both the region and the world."
Leaders from across Central and Eastern Europe as well as further afield, including a group of US lawmakers, were meeting in the Bulgarian capital Sofia at a two-day summit of Three Seas Initiative countries.
The event aimed to focus on issues including "a new shape of transatlantic relations" as Europe emerges from the coronavirus pandemic, according to Krzysztof Szczerski, a top aide to Polish President Andrzej Duda.
President Andrzej Duda. Photo: PAP/Radek Pietruszka
The Three Seas Initiative brings together Poland, Austria, Bulgaria, Croatia, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Romania, Slovakia and Slovenia.
The initiative’s key partners are Germany, the European Union and the United States, with France, Britain, Greece and Japan also interested in teaming up, according to Polish officials.
Earlier this year, Biden declared he wanted closer cooperation with Central Europe when he spoke with the leaders of NATO’s eastern-flank states during a virtual summit co-hosted by the Polish president.
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Source: PAP, IAR