Polish President Bronislaw Komorowski approved a resolution Monday that gave his formal consent to the establishment of a joint Polish-Lithuanian-Ukrainian military unit, his office confirmed. The joint brigade will serve separately from the three countries’ military commands, but will participate in NATO, United Nations and European Union operations.

Troops assigned to the joint brigade will be housed at its headquarters in Lublin, Poland, Russian news agency Tass reported. The Polish-Lithuanian-Ukrainian unit will consist of 4,500 troops. Plans call for the force to be fully operational by 2017, with preliminary joint drills scheduled for later this year.

So far, only a small part of Poland’s contribution to the force has arrived in Lublin. Ukraine and Lithuania have yet to send their troops. Komorowski will formally ratify Poland’s resolution in two weeks.

Poland, Lithuania and Ukraine announced their intention to form the brigade last September in response to Russia’s recent military aggression in Eastern Europe. The three nations had discussed the idea since 2007. Russian President Vladimir Putin ordered the annexation of Crimea last March after pro-European Union protesters forced former Ukrainian President Viktor Yanukoych, who was loyal to Moscow, to resign from his office.

The Polish-Lithuanian-Ukrainian brigade could serve on U.N. peacekeepers or participate in NATO operations if necessary, Komorowski said last September. “This is part of a wider plan … to support Ukraine, among others, in the area of modernization,” he said, as Reuters.

Western and Eastern European leaders have also accused the Kremlin of providing direct support to pro-Russian separatists active in eastern Ukraine in a conflict that has killed more than 6,000 people since last year. Russia has repeatedly denied involvement.

NATO formed an expanded rapid response force earlier this year as a check against Russia’s military expansion. The military alliance’s force consists of 30,000 troops, including a 5,000-soldier “rapid reaction force” that can be deployed in less than two days.