Tunisian authorities today blocked the first migrant boat headed for Italian shores under a deal between Rome and Tunis agreed last month, Italian Interior Minister Roberto Maroni said.

"Tunisian authorities have for the first time stopped a boat laden with illegal immigrants and brought it back to Tunisia," Maroni told reporters.

"It shows the agreement between our two governments works," he said.

Italy and Libya signed an agreement on April 5 under which some 20,000 Tunisian migrants who had already arrived in Italy would be given temporary residence permits while any subsequent arrivals would be sent back.

Tunisia also agreed to beef up security along its shoreline.

Italy's decision to grant permits to the migrants sparked anger in France, where thousands of the French-speaking migrants were headed.

Italy and France have since proposed changes to the EU's visa-free system that would limit freedom of movement within Europe in some cases.