Croatian prime minister Ivo Sanader announced at a special news conference in Zagreb on July 1 2009 that he is resigning and withdrawing from politics, international and Croatian media reported.
His resignation means that, by Croatian law, his cabinet is out of office too.
After official notice of the resignation has been forwarded by the president of parliament to president Stjepan Mesic, Mesic will consult the majority in parliament and appoint a new prime minister who will have 30 days to confirm that he or she commands a majority in parliament.
If this does not happen, parliament will be dissolved and elections held, Croatian site Javno said.
Earlier, Croatian media had speculated that Sanader, who has been prime minister since 2003 and won a second term in 2007, would stand for president in 2010.
But Sanader, leader of the centre-right Croatian Democratic Union, told the news conference:
"My job has been done, my political life ends now," the BBC said.
Croatia joined Nato in April 2009 but its European Union aspirations have been blocked by a border dispute with neighbouring Slovenia. European Enlargement Commissioner Olli Rehn has been attempting to resolve the dispute, but the Czech EU Presidency, which left office at the end of June, recently cancelled a meeting on the border dispute.
Media reports at the time said that the EU had lost patience with the prolonged dispute and wanted the two countries to come up with a solution bilaterally.
Sanader said that he wanted Jadranka Kosor, deputy prime minister, to succeed him.
Sanader rejected media reports that he was resigning for health reasons, but did not say why he was quitting.