Libyan coastguard left two women and a small boy aboard a boat they intercepted during a rescue operation and sank it, causing one of the women and the child to perish, Spanish NGO Proactiva Open Arm said on Tuesday.
Libyan coastguard claimed to have saved 158 migrants in the Mediterranean operation and to have them given medical and other humanitarian assistance, Proactiva Open Arms founder Oscar Camps tweeted.
"What they didn't say is that they left two women and a small boy on board and sank the boat because the women didn't want to board the rescue vessel," read the tweet.
"When we arrived at the scene, one of the women was still alive but we could do nothing to save the other woman and the little boy, who may have died hours earlier," the tweet added.
Camps's tweet contained a graphic photo of the woman and child's corpses floating in the sea amid wreckage from the boat.
"How much longer must we struggle against assassins who are enrolled by the Italian government to kill?" he asked.
The Italian government has banned charity rescue ships from docking at Italy's ports and has said operations to save migrants off Libya must be carried out solely by Libya's coastguard, which Italy is helping train and is supplying equipment to.
Libyan coastguard have intercepted around 10,000 people in the Mediterranean this year and returned them to shore while over 1,440 migrants have perished as they attempted to cross to Europe, according to the United Nations.