Greece has arrested a Croatian businessman wanted in connection with the fugitive war crimes suspect General Ante Gotovina.
Hrvoje Petrac and four other Croats are banned from the EU
The Croatian justice ministry has now asked Greece to extradite Hrvoje Petrac, 50, who was held on Wednesday in north-western Greece.
He was on a boat heading for Italy. He has been sentenced in absentia to six years in jail for kidnapping a boy.
Croatia suspects Mr Petrac of being a key protector of Gen Gotovina.
The European Union has postponed talks on Croatia's EU entry because of Zagreb's failure to arrest Gen Gotovina.
He has been indicted by the International War Crimes Tribunal in The Hague, accused of murdering Serb civilians during an operation to expel Serb forces from the Krajina region of Croatia in 1995.
Earlier this year Mr Petrac - now held in the port of Igoumenitsa - was sentenced in absentia by a Zagreb court for kidnapping the son of a former Croatian deputy defence minister and holding him to ransom.
The Croatian Foreign Minister, Kolinda Grabar-Kitarovic, was in Brussels this week explaining what Croatia was doing to locate Gen Gotovina.