The participants in the 59th annual session told Bosnia and Herzegovina, Montenegro and Macedonia that NATO's door would remain open only if they met the criteria and carried out the reforms.
They "all know that NATO's door is open for them as well if they demonstrate a new resolve to settle old differences, a track record of reform and responsibility, and political commitment to building security and stability together with their neighbours," said NATO Secretary-General Anders Fogh Rasmussen.
Over the past decade, Slovenia, Croatia and Albania walked through NATO's open door, he said, adding that Croatia's recent European Union accession "is an important step in the steady integration of South-East Europe within the Euro-Atlantic area."
NATO Parliamentary Assembly President Hugh Bayley said huge progress had been made in the region this year with Croatia's EU accession on July 1 and the historic agreement on normalisation of relations between Serbia and Kosovo.
Other regional countries are taking the same path and I know I can count on Croatia as an advocate of EU and NATO enlargement, he said.
Stressing that Croatia had achieved its strategic goals by joining the EU this year and NATO in 2009, Croatian President Ivo Josipovic said that, together with allies and friends, it would continue to build peace and stability in the region and the world.
"This orientation does not stem only from the wish to strengthen our security but from the deep conviction that peace can be achieved only by strengthening democracy," he said, warning that the strengthening of extremism and undemocratic manifestations would be dangerous to peace and security.
The host of the session, Croatian Parliament Speaker Josip Leko, said that through parliamentary and classic diplomacy, regional and cross-border cooperation Croatia wanted to positively impact the political and economic situation in the countries in the region and extend them all the necessary help.
"Croatia views its membership of European and Euro-Atlantic institutions as a unique historic opportunity for further development of democracy, stability and security. We believe that it is also an opportunity for the rest of South-East Europe and for other Mediterranean countries as well," Leko said.
Over the next three days, about 300 parliamentarians from 28 NATO countries will discuss the burning international crises in Syria and the Middle East, Afghanistan's future after the withdrawal of international troops in 2014, the strengthening of NATO's military capacity and the "smart defence" concept, which is expected to enable the downsizing of the member countries' defence systems in times of economic crisis.
With about 600 participants, this annual session is the biggest international conference ever held in Croatia, NATO's youngest member. On Monday, the last day of the meeting, the Parliamentary Assembly will adopt political recommendations on certain issues and forward them to the secretary-general and the North Atlantic Council. They will be important when the alliance's future is decided at a summit in Great Britain next year.