Tzotzis added that Petrac was accompanied by two Croatian citizens whose identity he could not disclose in the interest of the investigation.
Quoting official sources in the Greek police and coast guard, Reuters reported that Petrac was arrested by the Greek coast guard.
The news agency quoted an anonymous member of the coast guard as saying that Petrac was being interrogated.
The official would not say if Petrac was arrested while boarding the ferry or while disembarking.
The police in Athens confirmed the report about the arrest, but added that the case was in the jurisdiction of the coast guard.
Answering reporters' questions, Croatian government spokesman Ratko Macek said in Gdansk today that the government "will not comment on the news of the arrest of Hrvoje Petrac, but it can only say that all points of the government's Action Plan are being carried out".
Macek said that all details would be made known by the Ministry of the Interior.
Petrac's attorney Marijan Pedisic said he did not want to comment before obtaining official information.
Petrac, for whom Interpol issued an arrest warrant, has been on the run since the kidnapping of the underage son of General Vladimir Zagorac in February last year. A year later the Zagreb County Court ruled that he masterminded the abduction and sentenced him to six years in prison.
Petrac was mentioned as a person with connections in the underworld for the first time at the trial of a Zagreb crime ring. Several witnesses named him as a connection between mobsters and some public and political figures. Although he was not sentenced at the time, Petrac was unavailable to police during the whole trial and returned to Zagreb only after the court dismissed the prosecution's allegation about the existence of such criminal organisation.
During the one and a half years while on the run, Petrac sent a letter to the Croatian parliament's human rights committee through his attorney, complaining that he was prevented from protecting his rights, namely from submitting an appeal due to lack of an integral verdict.
The committee in late May this year informed the Justice Ministry of Petrac's objections, one of which was that the authorities, media and secret services were calling him the key figure of organised crime in the country and a helper of fugitive general Ante Gotovina.