Charities have branded the actions of the Italian government “illegal” after it prevented 250 people disembarking two migrant rescue ships.
There are 215 blocked on the Geo Barents and 35 on Humanity 1.
Children and people with medical issues were allowed to leave the ships in Catania, Sicily, but others were not. Two other rescue boats remain at sea.
The new Italian PM has promised to crack down on migrants travelling across the Mediterranean.
Italy is one of the main entry points into Europe and since the start of the year 85,000 migrants have arrived on boats, according to the UN.