KRAKOW, Poland, Feb 20, 2009 (Xinhua via COMTEX News Network) -- NATO Secretary General Jaap de Hoop Scheffer expressed concern on Friday that politics in Slovenia might prevent Croatia from formally joining NATO at a summit in early April.

"It gives me reason for concern that we might not see a situation at the summit in Strasbourg and Kehl that we can greet Albania and Croatia in the NATO family," he told a press conference at an informal NATO defense ministers' meeting.

"I think everyone involved, including in Slovenia, should do everything they can to make that happen," he said.

But he added that Slovenia could not be blamed for being a democracy. "You can't blame Slovenia for being a democracy and for having democratic means whenever a nation decides that those means should be used," said de Hoop Scheffer, referring to a petition of two nationalist groups in Slovenia for a referendum on Croatia's NATO membership.

Slovenian lawmakers approved Croatia's entry into NATO last week. But two nationalist groups in Slovenia, which are opposed to Croatia's NATO entry because of territorial disputes between the two countries, then filed an application for a referendum. A "no" vote in a referendum would annul the lawmaker's approval.

The groups now need to get 40,000 signatures to make a referendum happen. But even if a referendum were not ultimately possible, Croatia's accession might be delayed as the two political groups have at least five weeks to collect signatures from Slovenian citizens. The NATO summit was barely six weeks away when the petition was filed.

Slovenia and Croatia have not been able to completely draw their land and sea borders since their independence from the former Yugoslavia in 1991.