At least 14 migrants have died after a boat carrying hundreds of people sank in international waters north of Libya, according to the Italian navy.
At least 200 people have been rescued, but the Navy said it is unclear how many were aboard the smugglers' boat so the number of possible missing passengers is not known.
The Italian coastguard said the sinking occurred 65 kilometres north of the Libyan coast.
A coastguard official earlier said 200 people had been rescued and Italian media said around 400 people had been on board.
The coastguard said the rescue was being carried out by two commercial ships that were scrambled to the area, 185 kilometres south of Lampedusa island, Italy's southernmost point. The navy said it had dispatched a helicopter and two warships "at maximum speed" to give assistance.
The La Repubblica daily said Italy's coastguard was alerted to the incident by the crew of a ship involved in offshore oil extraction in the area.
A Libyan navy spokesman, Colonel Ayub Kassem, said Libya "does not have the means to help with this shipwreck, which took place in international waters".
Kassem said he could not confirm that the migrant boat had departed from Libya.
In another migrant boat shipwreck last Tuesday that was reported by the Libyan navy on Sunday, 36 migrants died and 42 were missing. Around 50 people were rescued.
More than 400 migrants drowned in twin tragedies off Lampedusa last year and immigration charities estimate that up to 20,000 migrants have died at sea trying to reach Europe over the past 20 years.
Hundreds of migrants have been landing in Italy on an almost daily basis in recent weeks, many of them now being picked up on Italian warships.
Agence France-Presse and Associated Press