Zagreb -- Croatia's Prime Minister Ivo Sanader resigned and quit politics on Wednesday, only hinting at frustration with his country's delayed EU membership bid as a reason for the shock announcement.

"I have decided to withdraw from active politics and will not run as a candidate for Croatian president" in elections due this year, Sanader told a hastily arranged media conference.

"Thank God I am not ill ... and I admit that I did not accept offers for engagement in European Union institutions," he said without elaborating on the move to journalists.

He said his party was to propose Deputy Prime Minister Jadranka Kosor as his immediate successor to President Stipe Mesic.

The move comes after the European Union stopped accession talks last week with Zagreb due to a border row with neighbouring Slovenia, which has blocked the EU process since December.

Asked whether his announcement was prompted by Croatia's stalled EU entry process, Sanader admitted the issue had contributed to his decision.

"I certainly also had that in my mind while I was considering this decision," he said.

"The EU... and project of European integration have no chance if the principle of blackmailing is accepted as a principle of acting within the EU," he said referring to Ljubljana's blockade of the talks.

Local political analysts voiced surprise over the unexpected announcement, stressing that the reasons for it were still not clear.

"If the reasons are political, it would be equivalent to abandoning a boat in rather heavy seas," analysts Ivan Siber said in reference to delicate political and economic situation the former Yugoslav republic was facing.

Under Sanader, Croatia started membership talks with the European Union 10 years after the end of its war of independence from the former Yugoslavia.

The country, which joined the NATO military alliance earlier this year, is hoping to become the European bloc's 28th member by 2011.

"I'm leaving satisfied since Croatia's strategic goals have been achieved," Sanader said.

"In life there are moments for new beginnings. I concluded that such a moment has come for me.

"I did my part, now the time has come for others. That is the rule of life and politics," said Sanader, who appeared relaxed as he made his announcement.

Sanader, 56, became prime minister in 2003 when his Croatian Democratic Union (HDZ) returned to power.

Since taking over the HDZ helm in 2000, Sanader has steered the party away from the nationalist bent it had under Croatia's late autocratic president Franjo Tudjman and put it among Europe's mainstream conservatives.

Rusmir Smajilhodzic/AFP/Expatica