Montenegro Prime Minister Milo Djukanovic says NATO's membership invitation represents a historic day for the tiny Adriatic state, the most important since the 2006 independence referendum.

Djukanovic said Wednesday "Montenegro is entering the exclusive circle of states which are synonymous with the highest values of modern civilization."

NATO member states on Wednesday formally invited Montenegro to join the alliance in the face of Russian opposition.

Djukanovic says "this is a crown jewel of the long-standing national efforts and comprehensive reform processes launched in 2006."