President Karol Nawrocki made the remarks after the talks in the Romanian capital, where regional leaders adopted a joint declaration identifying Russia as the most immediate threat and reaffirming backing for Ukraine.
The B9 summit brought together leaders from NATO's eastern members along with NATO Secretary-General Mark Rutte and officials from Nordic countries, including Danish Prime Minister Mette Frederiksen and Finnish President Alexander Stubb.
Speaking at a joint news conference with Romanian President Nicușor Dan and Rutte, Nawrocki said NATO's Ankara summit on July 7-8 should send a "clear signal of political unity and military strength."
Leaders agreed that increasing defence spending to 5 percent of GDP, as pledged at last year's NATO summit in The Hague, remains a key priority, along with continued support for Ukraine as it defends itself against Russia's invasion.
Rutte said the meeting of allies from the Black Sea to the Arctic demonstrated unity and determination to defend against threats from any direction, adding that Russia remains NATO's most significant and direct threat.
He said the Ankara summit would focus on military readiness, strengthening defence industries and maintaining strong support for Ukraine.
'No NATO without US'
Nawrocki also stressed the importance of transatlantic ties, saying "there is no NATO without the United States" and that unity, responsibility and cooperation across the alliance are essential for deterrence and security.
He warned that Russia was rebuilding its military capabilities and expanding infrastructure near NATO's eastern borders, including in Belarus, while engaging in hybrid activities in the Baltic region.
"Unity of the alliance is a moral obligation," Nawrocki said.
The leaders also highlighted support for Moldova's European integration and efforts to reduce its dependence on Moscow, Polish state news agency PAP reported.
On the sidelines of the summit, Nawrocki met with Ukrainian President Volodymyr Zelensky.
After the meeting, Nawrocki said he may visit Kyiv in 2027 and noted that an international conference on Ukraine’s postwar reconstruction would be held next month in the Polish Baltic city of Gdańsk.
He also announced that next year's B9 summit will be held in Warsaw.
The Bucharest Nine, established in 2015, brings together nine NATO countries on the alliance's eastern flank to coordinate positions on security issues.
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Source: IAR, PAP