Nineteen people died trying to reach Italy on a boat packed with hundreds of migrants, probably poisoned by carbon monoxide fumes from its engines, said the Italian Navy on Saturday, which has rescued more than 4,000 migrants in the last three days.

Eighteen bodies were found in the hold of the boat, said a navy spokesman, along with three very ill men who were rushed to the Italian island of Lampedusa but one died en route.

The two surviving men were taken by helicopter to a hospital in the Sicilian capital of Palermo, the spokesman said.

He said carbon monoxide fumes produced by the boat's engine likely caused the deaths. A similar incident last month killed 30.

Italy is struggling to keep up with the number of migrant boats this year, which mostly depart from the coast of increasingly unstable Libya, and is seeking more help from the EU in both the rescue mission and in hosting new arrivals.

The United Nations refugee agency (UNHCR) estimates that more than 500 migrants have died in the Mediterranean so far this year, compared to 700 during the whole of last year.

AGI news agency reported on Saturday that as many as 40 people could be missing after an incident on Friday when a migrant boat capsized near the Libyan coast. The Italian navy could not immediately confirm the report.

More than 70,000 migrants have been rescued by Italy's "Mare Nostrum" or "Our Sea" mission in 2014, the spokesman said, surpassing the previous record of just over 60,000 for the whole of 2011, when the Arab Spring uprisings fuelled arrivals.

Calmer summer seas have prompted a recent upsurge in boats trying to reach Italy, where immigration centres are overloaded. Interior Minister Angelino Alfano on Saturday said military bases might be temporarily used to house new arrivals.

Italy's navy has been patrolling the waters between Africa and Sicily since October, when 366 people drowned after their boat capsized just a mile from the Italian coast.

That tragedy focused international attention on the desperate risks taken by many migrants, whose plight has been highlighted by human rights groups and Pope Francis.

SHARING THE BURDEN

Italy has long attracted sea-borne migrants from Africa, and most move on almost immediately to other EU countries.

Over the past year, most of the migrants have been refugees fleeing Syria's civil war and Eritrea's harsh military service, according to the UNHCR.

Italy - along with Spain, Greece and Malta - have been left mostly on their own to manage the growing number of migrants, partly because increasing anti-immigrant sentiment in countries like Britain and France makes it unpopular to help out.

Alfano has begun talks with EU Home Affairs Commissioner Cecilia Malmstrom about sharing the burden of rescuing migrants in what she described as a "scaled-down" version of Mare Nostrum earlier this month.

"We are taking important steps to make sure that all of Europe is present in the Mediterranean, and not just Italy," Alfano said on Saturday. - Reuters