COLOGNE, Germany — The governments of Estonia, Latvia and Lithuania have agreed to tighten their defense cooperation, vowing to explore the joint acquisition of new rocket launchers amid fears of Russian military moves in their neighborhood, the countries said in a joint declaration.

The Monday announcement follows a May 21 meeting of the three defense ministers in Siauliai, Lithuania, meant as a stepping stone toward the June 14 NATO summit in Brussels.

“We thoroughly discussed the expectations for the forthcoming NATO summit with our Baltic colleagues,” Estonian Defence Minister Kalle Laanet said in a statement circulated by his agency. “We believe that NATO needs to send a clear and strong message about the Russian threat and make collective defense the most important task of the alliance in the next decade.”

Joint weapons acquisition has been on the agenda for increased Baltic cooperation for some time. The countries have now decided to begin preparatory work toward a multiple-launch rocket system, according to the joint declaration. The weapon would enter service sometime after 2025.

“I have previously emphasized that cooperation in the field of capability development between Estonia, Latvia and Lithuania has a great deal of potential and an extremely important role in strengthening security in the region,” Laanet said. “The development of strategically important capabilities is resource-intensive, which is why we need to think carefully about how to ensure the most efficient realization of limited resources.”

The three defense ministers stressed air defense as a vital capability that they want to see strengthened in concert with NATO. Baltic officials have lobbied for years that the alliance expand its air-policing program in the region into a more comprehensive umbrella against all manners of aerial threats.

Estonia, Latvia and Lithuania, formerly part of the Soviet Union, encompass a key strategic area on NATO’s eastern flank. Russia’s annexation of Crimea from Ukraine in 2014 stirred fears in the three nations that Russia could use tactics employed during that operation in a surprise move against the Baltics.

The countries’ joint declaration makes clear they perceive the simmering conflict in eastern Ukraine with a sense of foreboding. They call for an uptick in international military assistance to Ukraine and Georgia, with the idea of strengthening their defense and resilience while enhancing interoperability with NATO nations.

The three governments welcomed “consultations” between the United States and allies about the Pentagon’s ongoing global force posture review, highlighting American troops on NATO’s eastern flank as “one of the main and most viable means of defense against aggressive and revisionist Russia.”