All the rescues were carried out on Wednesday, the official said, with no details about the one death or the migrants' nationalities. No boats had yet been spotted on Thursday as sea conditions worsened, he said.

With Libya engulfed in strife, people smugglers are increasingly free to pack migrants onto unsafe boats, and they are expected to push total arrivals in Italy for 2015 to 200,000, an increase of 30,000 on last year, according to an Interior Ministry projection.

Italy is bearing the brunt of the Mediterranean rescue operation while European Union authorities press other member states to share the burden more fairly via a resettlement quota system for refugees.

Two Italian coast guard patrol boats and a merchant ship whose country of origin was not given saved 328 migrants from a boat in Maltese waters on Wednesday. A French navy vessel participating in the EU's border control mission Triton picked up 297 people, including 51 women and children.

Finally, an Italian navy ship rescued 286 and picked up one body. All of the migrants have been or will be brought to Italian ports, the coast guard said.

Refugees escaping war and political persecution, and economic migrants desperate for a better life have been pouring into Italy this year, with approximately 35,500 arriving there up to the first week of May, the UN refugee agency estimates.

Also including arrivals in Greece, Spain and Malta, a total of 62,500 have reached Europe by boat, with Syrians making up a third and Afghans and Eritreans 10 percent each.

The number of dead or missing this year is about 1,800 compared with 3,500 during the whole of last year, the United Nations High Commissioner for Refugees says.