An Italian prosecutor says he has evidence some of the charities saving migrants in the Mediterranean Sea are colluding with people-smugglers.
Carmelo Zuccaro told La Stampa (in Italian) phone calls were being made from Libya to rescue vessels.
Organisations involved in rescue operations have rejected accusations of collusion, saying their only concern is to save lives.
Italy is the main route for migrants trying to reach Europe.
Almost 1,000 people are thought to have drowned in waters between Libya and Italy this year, according to the UN refugee agency.
Nearly 37,000 people have been rescued over the same period, a surge of more than 40% from last year, the figures say.
“We have evidence that there are direct contacts between certain NGOs [non-governmental organisations] and people traffickers in Libya,” Mr Zuccaro is quoted as saying in La Stampa.