Sharjah24 - AFP: About 30 migrants were missing and presumed drowned after the overloaded boat they were on capsized during a rescue attempt by a cargo ship off Libya, Italy's coastguard said on Sunday.

Seventeen migrants were saved and a search was underway for the missing after the early-morning attempted rescue in Libya's search-and-rescue zone, the coastguard said.

"During the rescue operations... the boat capsized during the transfer of the migrants: 17 people were rescued and recovered by the (cargo) vessel while approximately 30 migrants were missing," said the coastguard.

The latest disaster in the Mediterranean comes exactly two weeks after a shipwreck off Italy's southern coast of Calabria that killed at least 76 migrants, with bodies continuing to wash ashore nearly daily.

That shipwreck has put Italy's right-wing government led by Prime Minister Giorgia Meloni on the defensive as it tries to fend off sharp criticism that it failed to intervene in time to save the migrants.

Sunday's botched rescue is sure to increase finger-pointing over who is to blame for deaths even as an increasing number of migrants embark on the perilous Central Mediterranean crossing headed for Italy's shores.

Italy's coastguard said the boat in distress was in Libya's search-and-rescue zone, and that the deadly episode laid bare "the inactivity" of other countries in the Mediterranean.

Rome has long complained to its EU partners that it bears the brunt of the tens of thousands of migrants seeking to reach Europe by boat each year.

First to be alerted to the boat in distress some 100 miles (160 kilometres) northwest of Benghazi was Alarm Phone, a charity that monitors migrant boats. It said it then alerted Italian authorities at 0118 GMT Saturday morning.

A surveillance plane of German NGO SeaWatch also spotted the boat and reported it was "dangerously overcrowded and in frightening waves".

In a statement, Italy's coastguard confirmed that Alarm Phone had notified Rome's rescue coordination centre, as well as Maltese and Libyan authorities, about the boat.

A merchant vessel that had headed towards the boat after the alert by SeaWatch reported difficulty in rescuing the boat due to bad weather, the coastguard said.