By Isla Binnie

ABOARD ITALIAN WARSHIP GARIBALDI (Reuters) - The leaders of the euro zone's biggest economies held talks on Monday in the aftermath of Britain's shock decision to leave the European Union and said Europe had to turn its back on populists who blamed Brussels for all its problems.

Speaking on an aircraft carrier off the Italian island of Ventotene, Germany's Angela Merkel, France's Francois Hollande and Italy's Matteo Renzi issued calls for closer security cooperation and better opportunities for young people.

In a meeting heavy on symbolism, the three leaders visited Ventotene to lay a wreath on the tomb of Altiero Spinelli, an Italian intellectual seen as a founding father of European unity.

They then boarded the Garibaldi, which is in the front line of an EU mission to combat people traffickers who have carried hundreds of thousands of migrants to Europe across the Mediterranean.

"For many populists, Europe is to blame for everything that goes wrong," Renzi said at the joint news conference before the leaders sat down for talks aboard the ship.

"Immigration, it's Europe's fault, the economy is bad, it's Europe's fault. But that is not the case."

The meeting was designed to lay the groundwork for an EU summit in Bratislava next month.

Monday's talks marked the beginning of a week of meetings for Merkel with other European governments that will see her travel to four countries and receive leaders from another eight.

"We respect Great Britain’s decision but we also want to make clear that the other 27 (member states) are banking on a safe and prospering Europe," the German chancellor said.

DIVISIONS

But questions of how to bring about prosperity have divided the three countries.

Heavily-indebted Italy, whose economy has barely grown since the introduction of the euro currency in 1999, has repeatedly chafed against stern EU budget rules, and both Renzi and Hollande want greater flexibility to help boost growth.

Germany is keen for rules to be respected, and Renzi and Merkel sidestepped a question on deficit limits.

All three leaders are threatened at home. Merkel faces discontent over her controversial decision to let in a million mainly Muslim migrants last year.

France is reeling from a wave of Islamist attacks and Renzi faces a referendum on constitutional reform this autumn that could trigger his downfall.

The EU plans to offer incentives to African governments to help slow the flow of migrants into Europe, but divisions among member states are stark.

Italy, the main entry point for Africans but rarely their planned destination, is struggling to house migrants turned back from neighboring countries including France, and disagrees with Germany over how to finance the response.

Hollande stressed the need to protect the EU from militant violence by tightening borders and sharing intelligence.

"To have security we need frontiers that are controlled so that is why we are working to reinforce coastguards and border guards," he said. "We want more coordination in the fight against terrorism."

(Additional reporting Michelle Martin in Berlin, John Irish in Paris; Writing by Gavin Jones and Crispian Balmer; Editing by Philip Pullella and Andrew Roche)