"After more than two days of searching, we have found no more bodies or survivors or the boat," a Libyan official told the Reuters news agency.
The office of the UN High Commissioner for Refugees (UNHCR) in Geneva said on Tuesday that Egyptians, Tunisians and Africans were on board the boats that were wrecked around 30km off the Libyan coast.
"This is the beginning of the smuggling season in the Mediterranean"
Libyan officials said it was not clear whether the boats left for Italy from Libya.
Libya, which has 1,770km of coast, is a popular departure point for African migrants trying to reach Europe for a better life.
"This is the beginning of the smuggling season in the Mediterranean," Ron Redmond, the UNHCR spokesman, said.
"This tragic incident illustrates, once again, the dangers faced by people caught in mixed irregular movements of migrants and refugees in the Mediterranean and elsewhere which every year cost thousands of lives."
The report of the deaths comes amid plans by Italy and Libya for a joint sea patrol in May in a bid to halt the influx of migrants trying to reach European countries.
The Italian interior minister said on Monday that the patrols would begin on May 15, and he expected that day to "mark the end" of illegal migration from North Africa.
"We have done everything possible to prevent arrivals," Roberto Maroni said.
"We have signed a deal with Libya and the Libyan government is committed to launch on May 15 patrols along the coasts with six vessels.
"Until then, we will continue to ask the Libyan authorities to intensify controls, but I guess that there will still be arrivals."
Hart, of the IOM's Tripoli office, said that the agreement may have been a "push factor which people smugglers exploited telling would-be migrants: "it is now or never".
Nearly 37,000 immigrants deemed illegal landed on Italian coasts last year, a 75 per cent rise from 2007, according to the Italian interior ministry.
Rights groups say most migrants risk their lives in treacherous waters trying to reach Europe hoping to escape poverty in their home countries.