"I especially emphasise Croatia, as the country is experiencing a political crisis, and I hope that the government and the parliament will do their part of job, regardless of the ongoing problems," the Slovenian diplomat told the Podgorica-based "Pobjeda newspaper on Friday.
To date, the legislatures of Slovenia and Iceland ratified the document. The Slovenian parliament ratified Montenegro's NATO accession protocol by a vast majority of votes on 8 June.
Iceland was the first country to recognise the independence of Montenegro 10 years ago.
Montenegro will be the third country from the area of the former Yugoslavia and the fourth Balkan state to join NATO, Kacin noted.
His country was the first ex-Yugoslav republic to enter the alliance in March 2004. Croatia did it in 2009 when Albania was also admitted.