At least 21 migrants from Africa died when their boat sank off Tunisia as they tried to cross the Mediterranean to the Italian island of Lampedusa, a Tunisian official said on Friday.

An air strike hit a detention centre for mainly African migrants in a suburb of the Libyan capital Tripoli late on Tuesday, killing at least 44 people and wounding more than 130, the United Nations said.

A charity rescue vessel carrying 311 mainly African migrants plucked off Libya docked in Spain on Friday, ending a traumatic journey which saw them spend Christmas at sea and several European nations denying the ship entry.

Libya is a major departure point in North Africa for migrants crossing the Mediterranean Sea to Europe, mainly from other parts of Africa.

France will grant asylum to around 80 refugees from the Aquarius rescue vessel which was at the centre of a bitter European dispute over migration last month, the country's asylum office said Tuesday.

Dozens of Africans say they were sold for labour and trapped in slavery in Algeria in what aid agencies fear may be a widening trend of abusing migrants headed for a new life in Europe.

Israel's Supreme Court on April 10 gave the government until Sunday to finalise a deal it said it was working on to deport some of the migrants to another country.

Israeli Prime Minister Benjamin Netanyahu said on Tuesday he was cancelling an agreement with the UN refugee agency to relocate thousands of African migrants, bowing to right-wing pressure to scrap the deal.

The United Nations on Tuesday called on Israel to scrap a new programme forcing thousands of African migrants out of the country, condemning it as incoherent and unsafe.

A French farmer, who has become a folk hero for helping African migrants slip across the border from Italy and giving them shelter, went on trial Wednesday for aiding illegal arrivals.

Encouraged by their success in halting a mass influx of refugees by closing Greek borders and cutting a controversial deal with Turkey, EU leaders are getting tough on African migrants too.

At least eight African migrants, and possibly as many as 27, died in a new boat tragedy off the coast of Libya, a search and rescue organisation said Monday.