NATO Secretary General Jaap de Hoop Scheffer says alliance expansion remains a necessity for the stabilization of Europe, and says NATO's door will remain open for future members.
De Hoop Scheffer spoke Thursday in Budapest, at ceremonies marking the 10th anniversary of Polish, Hungarian and Czech accession into the defense alliance.
The NATO chief said current and future challenges include the stabilization of Afghanistan, European energy security, cyber-crime and piracy. He also said NATO needs to improve its relationship with Russia, which remains opposed to alliance expansion closer to its borders, and opposes a U.S. plan to build a missile defense system on Polish and Czech soil.
NATO has strongly condemned Russia's invasion of Georgia last year.
De Hoop Scheffer said he expects those issues to be addressed next month at a NATO summit on the French-German border.
The NATO secretary general also noted that Albania and Croatia are due to gain alliance entry next month.