Malta's armed forces have taken control of a tanker that was hijacked by migrants it had rescued off Libya.

It said a special operations team escorted the vessel to Malta where it was "handed over to the police for further investigations".

The Palau-flagged tanker Elhiblu I picked up the migrants on Tuesday evening in waters where Libyan coastguards are responsible, and then headed back to Tripoli.

But six nautical miles from port the ship suddenly changed course and headed north toward Europe.

Italy's far-right Interior Minister Matteo Salvini said yesterday the vessel had been hijacked, and vowed that the migrants would not be allowed to disembark in Italy.

The tanker was about 30 nautical miles from Malta when the Armed Forces of Malta (AFM) established communications with the captain.

"The captain repeatedly stated that he was not in control of the vessel and that he and his crew were being forced and threatened by a number of migrants to proceed to Malta," the AFM said in a statement.

"AFM Patrol Vessel P21 stopped the tanker from entering the Maltese territorial waters.

"An AFM Special Operations Unit team was dispatched to board and secure the vessel in order to hand over control of the ship to the captain."

It said the team was backed up by several naval vessels and a helicopter.

The German charity Sea-Eye, whose ship Alan Kurdi was in the rescue zone off Libya and which overheard radio messages between a European military aircraft and the tanker, said the ship picked up 108 migrants including women and children.

Migrants in Libya face trafficking, kidnap, torture and rape, according to the United Nations and aid groups.

Following Italy's increasingly tough anti-migrant stance, boats that pick up migrants making the perilous journey across the Mediterranean increasingly return them to Libya.

Boatloads of rescued migrants have in recent months refused to disembark in Libya, prompting the authorities there to use force.

The European Union announced yesterday it would suspend ship patrols that have rescued tens of thousands of migrants in the Mediterranean and brought them to Italy, in the face of deep resistance from Rome's populist government.

Migrant arrivals from North Africa and the Middle East have been sharply reduced since a 2015 peak when Europe faced its worst migration crisis since World War II.