Launched in 2015 by Polish President Andrzej Duda and his Croatian counterpart, the project promotes cooperation primarily among former communist nations in the region.
On Tuesday, the 10th annual Three Seas Summit concluded in Warsaw, with heads of state from across Europe in attendance.
At the summit, Montenegro and Albania officially joined the initiative, while Turkey and Spain were welcomed as strategic partners.
Michał Owczarek reports.
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