APA quoted the Slovene president's press secretary, who did not give any explanation.
The Croatian president's office confirmed the postponement. It told Hina that the purpose of the meeting was to present a book written by the Slovene president.
Slovene media on Sunday quoted a Zagreb newspaper as saying that Mesic and Drnovsek were to meet in Bjelovar, about 80 kilometres northeast of Zagreb. Drnovsek's office confirmed the information the same day.
Slovene media reports said that the purpose of the meeting was to alleviate the tension between Ljubljana and Zagreb following an exchange of notes over concessions the Croatian government had granted to national oil company INA to prospect for oil and gas in the northern Adriatic.
At several of their meetings last year, the two presidents urged their governments to step up efforts to resolve the outstanding issues between the two countries.