Eight migrants died in the Mediterranean and 375 were rescued from small boats on Tuesday, aid group Proactiva Open Arms said.
More than 2,200 people died so far this year trying to make the crossing from North Africa to Europe while about 95,000 were rescued and taken to Italy.
“We are here to avoid more drownings, today another eight dead and four dinghies adrift,” Proactiva founder Oscar Camps wrote on Twitter, adding 77 women and 52 minors were among those rescued.
Non-governmental organisations (NGOs) now carry out about a third of all operations in the search-and-rescue zone north of Libya, according to Italy’s coastguard, which co-ordinates rescues.
Italy fears NGOs are facilitating people smuggling by hovering close to Libya, waiting for migrant boats to cross into international waters where they can be picked up.
Looking to impose clear rules on humanitarian groups, the Italian government has drawn up a code of conduct for sea missions. Proactiva was one of only three NGOs to back the plan, with five groups refusing to sign the document.