Rome - At least two boats carrying hundreds of African would-be immigrants have sank off the Libyan coast, with 21 bodies and 23 survivors recovered and hundreds more missing, officials said Tuesday.

It was not immediately clear how many people were on board the vessels or when the accident took place.

Earlier reports from Libya said one boat was carrying 257 people and the other had 340 on board.

At least 10 Egyptian nationals were among the dead, Egypt's Assistant Foreign Minister for Consular Affairs, Ahmed Rizq, told Egypt's official MENA news agency.

"We believe that between 200 and 230 people are still unaccounted for," Peter Schatzer, the representative in Italy for the International Organization for Migration, said.

The vessels, which were heading for Italy from Libya, are believed to have sank some 30 nautical miles off the Libyan coast, Schatzer told Italian television news channel Sky TG24.

Italian television reports also cited Libyan officials as saying that an Italian freighter picked up 350 people from a third boat which was discovered in distress.

Italian coast guard officials said they believed Libyan authorities were referring to a rescue operation on Sunday involving an Italian freighter, which picked up some 350 would-be immigrants stranded at vessel at sea and then carried them to the Libyan port of Tripoli.

On Monday more than 400 would-be immigrants landed in Sicily, as Italy's Interior Minister Roberto Maroni said such arrivals from the North Africa would stop once an agreement involving Libyan naval patrols comes into effect in May.

"There's a commitment by the Libyan government to begin patrolling its coastline with six boats beginning on May 15," Maroni said.

"I have no reason to doubt that this will happen and that hence the problem will be solved," he added.

According to Italian government figures, a total of 36,900 would- be immigrants arrived in Italy by sea in 2008, a 75-per-cent increase over the previous year. Of these some 31,000 landed on Lampedusa, an islet situated south of Sicily.