One of the boats, which is carrying 400 people and is in the Ionian Sea off the coast of Calabria, southern Italy, had previously been sighted in Maltese waters.

Earlier on Monday, German NGO Sea-Watch International, which had located the fishing boat with one of its planes, said one merchant ship in the area had supplied fuel and water to the boat in distress, but Maltese authorities had ordered it not to conduct a rescue.

Early on Sunday, support service Alarm Phone had said the vessel, which departed from Tobruk in Libya, was adrift and taking on water.

The Maltese authorities did not respond to several requests for comment.

The other rescue operation by Italian coast guard on Monday was to help a fishing boat carrying 800 people that was located over 120 miles southeast of Siracusa, in Sicily.

It said in a statement this operation was complicated by the number of people on board.

A spokesperson for coast guard said it would take hours to complete the two ongoing operations because of difficult conditions, including the long distance form the coast.

Before these two operations, the Italian coast guard had already rescued around 2,000 migrants since Friday, it said.