KIEV, Oct. 31 (Xinhua) -- The North Atlantic Treaty Organization (NATO) Secretary General Jens Stoltenberg on Thursday said the doors of the alliance are open for those who wish to join, including Ukraine.

"As a sovereign state, Ukraine has the right to choose its security systems. NATO membership is the decision of the members of the NATO Alliance and those who want to join it. The spheres of influence are a thing of the past," he told the Ukrainian Parliament.

Stoltenberg stressed that NATO advisers will help Ukraine to implement Euro-Atlantic principles and best practices to strengthen the rule of law, ensure minority rights and fight corruption.

Headed by Stoltenberg, the delegation of the North Atlantic Council, NATO's political decision-making body, was visiting Odessa and Kiev on Oct. 30-31.