At least 35 refugees, including seven children, were feared drowned after their inflatable boat sank on Saturday off the Libyan coast.
Eighty-five refugees, including 18 women, were rescued after clinging to the boat with the help of fishermen who alerted the Libyan coastguard, said Issa al-Zarrouk, a coastguard official in Garabulli, 60 kilometres east of Tripoli.
Navy spokesman Ayoub Kacem said the boat sank six nautical miles northwest of Garabulli, and 10 fishing boats took part in the rescue.
They were among 100 refugees on board when their rubber boat developed a malfunction off eastern Tripoli, he added.
Qasim said the rescued refugees were from Nigeria, Senegal, Cameroon, Ghana and Ivory Coast.
The official did not disclose the nationalities of those who were missing.
Nigerian hairdresser Vivian Effoussa described watching, horrified as fellow passengers fell into the sea.
"The boat we entered was leaking," said Effoussa, who attempted the crossing to Europe after struggling to support two children back home.
"All of a sudden... the water was (coming) inside. Everybody started shouting," she said, speaking in English.
"Gradually, gradually, we see ourselves inside the sea. Everybody, we're falling inside, dragging each other. They even pulled my hair, dragging me."
"Really, I didn't think the sea was big like this," Effousa said, adding that, had she known, she would not have come.
The incident is the latest in a series of tragedies involving migrants desperate to enter Europe via the Mediterranean Sea.
Libya is the main departure point for Europe-bound migrants. Many of them come from poor African countries.
Human traffickers have exploited years of chaos in Libya since the 2011 uprising that toppled and killed dictator Muammar Gaddafi to boost their lucrative but deadly trade.
Tens of thousands of migrants have resorted to paying smugglers to cross the Mediterranean Sea from Libya to what they hope will be a better life in Europe.
Nearly 77,000 migrants have landed in Italy since January, up 15 percent on the same period in 2016.
Altogether, at least 2,247 people have died or are missing after trying to cross the Mediterranean to Europe this year, the IOM says.
Meanwhile, the bodies of 20 Egyptian nationals were found by Libyan authorities in a remote area of the Tobruk desert.
The director of the Tobruk Medical Centre Faraj al-Gali said on Friday evening that the Tobruk medical centre morgue had initially refused to accept the bodies because they were decomposed, and feared the transmission of germs.
Colonel Maraqa Mohammed, head of the investigation unit of the illegal immigration agency, said that the bodies of the Egyptians were found south of the 200 gate near Wadi Ali, inside the sand area. They were brought from the desert by a number of civilian cars because there were no available government SUVs.
The bodies were buried after being searched by the Red Crescent in Tobruk. A number of cards, passports and a few personal belongings were found. The cause of death has not yet been identified.