In response to Russia’s seizure of Ukraine’s Crimea, Lithuania and Poland agreed on Thursday to revive a joint military brigade with the country and deepen defense cooperation.

The three former Soviet satellite states agreed as early as 2007 to erect a multinational unit but efforts stalled in recent years. Russia’s invasion and annexation of the Crimean Peninsula, which headquarters its Black Sea Fleet and has a majority ethnic Russian population, prompted the countries into action.

Lithuanian and Polish defense ministers Juozas Olekas and Tomasz Siemoniak met in Białystok in northeastern Poland on Thursday to discuss security in the region and the situation in Ukraine. According to a statement, “The ministers agreed to proceed with the bilateral cooperation between Lithuania and Poland, continue the existing projects and acquisitions and start new ones, especially in the field of air defense.”

Olekas also said he and Siemoniak agreed to continue development of the joint military brigade with Ukraine but cautioned that it was too early to discuss deployment.

The brigade, which is supposed to consist of up to 4,500 soldiers, would be available for military missions to the European Union and NATO.

Lithuania and Poland joined both the European Union and NATO after the Soviet Union collapsed in 1991. Ukraine is not a member of either bloc but signed part of an association agreement with the European Union on Friday — the very treaty that former president Viktor Yanukovich rejected, stirring months of protests against his government that culminated in his ouster and Russia’s intervention.

The country has also conducted joint exercises with NATO member states and contributed to Western anti-piracy and counterterrorism operations.

Poland has taken an active role in the Ukrainian crisis, first negotiating a fleeting compromise between Yanukovich and the opposition and then calling for NATO consultations when Russia invaded the country.

Russia has denied sending troops into the Crimea but said it had a right to intervene in Ukraine in order to protect Russian speakers there as well as its naval base at Sevastopol. Lithuania has a 5.8 percent ethnic Russian population. Many live in the port city of Klaipeda which is close to Kaliningrad, a Russian enclave wedged between Lithuania and Poland that headquarters Russia’s Baltic Fleet.