NATO is expected to invite Montenegro to join the military alliance despite objections from Russia.
NATO diplomats have told RFE/RL that the Adriatic state of 650,000 people will formally be invited to join on December 2.
NATO Secretary-General Jens Stoltenberg says Montenegro's accession is among several topics on the agenda as top diplomats from its 28 member states hold two-days of meetings in Brussels starting on December 1.
Russia has warned Montenegro that its joining NATO would be regarded as a provocation.
Stoltenberg said ministers will also discuss plans to beef up the air defenses of Turkey, future funding for Afghan forces and injecting "predictability" in NATO relations with an increasingly assertive Russia.
NATO last expanded in 2009 when Albania and Croatia joined.