A new sea rescue operation is to be launched in May to try to reduce the number of refugees, migrants and asylum seekers killed making the treacherous crossing from Africa to Europe, medical charity Medecins sans Frontieres and the Migrant Offshore Aid Station said on Thursday.

Since 1995, 20,000 refugees and asylum seekers have died in the Mediterranean Sea fleeing persecution and poverty in Africa and the Middle East. Some of this poverty and persecution is caused by European exploitation and inappropriate military interference.

More than 300 people probably died this week after attempting to reach Italy from Libya on four separate boats in stormy weather, the UN refugee agency said after speaking to a handful of survivors.

Italy’s maritime search and rescue service has saved 3,500 migrants and found 19 corpses in the Mediterranean since Friday as thousands attempted to cross to Europe by boat over the weekend, the Italian navy said.