At least 12 people died after a rubber boat which spent more than 10 days at sea capsized off Misrata, Libya, the UN migration agency has said, urging search and rescue operations to be stepped up in the Mediterranean.
Three other passengers from the boat remain missing, according to IOM.
"The survivors were all suffering from complete dehydration and exhaustion after being stranded at sea for days," said IOM physician Mohamed Abughalia.
"People suffered from trauma, severe malnutrition and burns sustained from the boat's engine fuel."
Four people in need of emergency medical care were transferred to a private hospital in Tripoli, IOM said.
Six others were moved to detention centres tun by Libyan authorities, where IOM continues to provide medical care and adequate assistance including mental health and psychosocial support to the survivors.
"There are is a higher probability of dying at sea now than one year ago. This is not acceptable," he said.
Supported by a reconnaissance aircraft, the fleet will carry out joint search and rescue in the central Mediterranean and document human rights violations, the charities said, accusing European Union countries of shirking their international legal obligations towards migrants.
"We do not want to live in a Europe that has turned its maritime border into a mass grave as a deterrent and has its Libyan bouncers do the dirty work," said mission chief Johannes Bayer.
"As long as the EU lets people drown in the Mediterranean, we will continue to go to sea."
The Sea-Watch 3 rescue vessel had been unlawfully detained in Malta for four months, Seawatch stated.
The last migrant rescue ship operating in the Mediterranean, the Acquarius, chartered by the Doctors without Borders (MSF) and SOS Mediterranee charities, has been stuck in Marseille's since Manama in September revoked the right to fly its flag, allegedly following a request from Italy's far-right, anti-establishment government.
(With inputs from agencies.)