NATO Secretary General Jens Stoltenberg has said that the alliance's open-door policy has been very successful in the past 20 years.

He said at the 60th plenary session of the NATO Parliamentary Assembly in The Hague on Monday that this had contributed to more democracy, stability, freedom and prosperity in new NATO allies and that the expansion had been a great success.

"The open door is still open, and it's something we decided. I remember the summit in Bucharest where we decided that Ukraine will become a member, and that decision still stands, of course, providing that Ukraine fulfills the criteria for membership and providing that Ukraine so will," Stoltenberg said

At the same time, he recalled that several years ago, Ukraine had decided to have a non-bloc policy and therefore the question of its membership of the alliance had not been on the table.

"It's up to each sovereign nation to decide itself what kind of security arrangements it would like to be part of. And therefore I respect this decision of Ukraine, but our policy is the same. The door is open," he said.

As reported, members of a future parliamentary coalition have recently included a provision in the coalition agreement stating that as part of reforming the national security and defense system Ukraine will give up its non-aligned status and resume integration into NATO.