The United Nations' Refugee Agency said in a statement it was deeply saddened by reports of an estimated 170 people dead or missing.
An estimated 170 migrants have been lost in the Mediterranean in two incidents involving dinghies that left from Libya and Morocco, migrants organisations said on Saturday.
One dinghy was spotted sinking in rough waters on Friday by an Italian military plane on patrol. The plane dropped two safety rafts into the water but had to leave due to a lack of fuel, Rear Admiral Fabio Agostini told TV channel RaiNews24.
A naval helicopter was dispatched and rescued three people who were suffering from severe hypothermia and taken to hospital on the island of Lampedusa.
"During this operation at least three bodies were seen in the water who appeared to be dead," Agostini said.
The three survivors said they had left Gasr Garabulli in Libya on Thursday night as part of a group of 120 people, mainly from west Africa, according to Flavio Di Giacomo, spokesman for the International Organisation for Migration (IOM).
"After 10 to 11 hours at sea ... (the boat) started sinking and people started drowning," Di Giacomo said, adding the passengers included 10 women and two children, one of whom was just two months old.
The Italian navy said it had alerted Libyan authorities who ordered a merchant ship to go to the site but the rescue effort was called off after the search proved fruitless.
In another incident, 53 migrants who left Morocco on a dinghy were missing after what one survivor said was a collision in the Alboran Sea, in the western Mediterranean, according to Spanish non-governmental organisation Caminando Fronteras.
The United Nations' Refugee Agency said in a statement it was deeply saddened by reports of an estimated 170 people dead or missing. It said it had been unable to independently verify the death toll.
Separately, the charity Sea-Watch said on Saturday it had rescued 47 people at sea, including eight unaccompanied minors, from a rubber boat in distress north of the Libyan city of Zuwara.
Matteo Salvini, Italy's interior minister, who has closed off Italian ports to humanitarian boats since a populist government came to power in mid-2018, said the ports would remain closed to deter human traffickers.
"The latest shipwreck is proof that if you reopen the ports more people will die," Salvini said in a video on Facebook on Saturday.
He said 100 people had reached Italy so far this year compared with 2,000 in the same period of 2018.
Migrant arrivals to Europe in the first 16 days of 2019 totalled 4,449, almost all by sea, compared with 2,964 in the same period of 2018, IOM data showed.
It said last year, some 2,297 migrants died or went missing in the Mediterranean while 116,959 people reached Europe by sea.