He was responding to questions from the press to comment on media reports that Petrac is in Israel.
Asked which measures had been taken, Mesic said "all the necessary measures".
According to the media, Petrac, who was sentenced to six years' imprisonment for the kidnapping of the underage son of General Vladimir Zagorac, has been hiding in Israel, where he has allegedly been seeking political asylum.
The media have also said that earlier this week Croatian judicial bodies delivered to Israel all the legal documents pertaining to the Petrac case, including an arrest warrant.
Asked when Petrac might be extradited to Croatia, Mesic said it was difficult to say because two countries were involved. He added the extradition procedure would be honoured and that it envisaged legal assistance to the extraditee.
Interior Ministry spokesman Zlatko Mehun declined to comment on media allegations and Mesic's statement that Petrac is in Israel.
In a brief statement to Hina, Mehun said the ministry did not comment on details pertaining to the Petrac case.
He said that under the law, the Croatian police cooperated with Interpol and other countries' police forces in all cases where an international arrest warrant had been issued, and that this was so in this case as well.