Thousands of people risk their lives to cross from Africa to Europe
Tunisian rescue teams have resumed their search for about 200 illegal immigrants who are feared dead after their boat capsized off the country's coast on its way to Italy.
The Tunisian coast guard has already rescued 41 people and recovered 20 bodies, but rough seas have hampered the rescue operation.
Survivors said the boat had been carrying about 250 people, believed to be from sub-Saharan Africa and northern Africa.
It is at least the second boat to go down in the area this week. As many as 70 were drowned when their boat sank off the tiny Italian island of Lampedusa on Monday.
Italian newspapers have described the stretch of water between Africa and Sicily as a huge underwater graveyard.
The cause of Friday's sinking is not known.
It may have been because the boat was overcrowded or in poor condition, or because of the bad weather - or a combination of all three.
A fishing boat raised the alarm at dawn on Friday when its crew saw the sinking ship.
The Tunisian national guard and navy responded, as did four civilian ships nearby and a pair of boats from offshore oil rigs in the area.
Officials have not said where the boat came from but survivors say they boarded in Libya, which is becoming a favourite spot of the ruthless immigrant-smuggling gangs, says the BBC's Frances Kennedy in Rome.
Italy this week accused Libya of being a base for boats trying to bring illegal immigrants across the Mediterranean.
Italy's long coastline makes it a popular landfall for people seeking to enter Europe illegally, with almost 3,000 believed to have landed in the country this month alone.
In the past week more than 1,000 migrants have arrived on Lampedusa, which is closer to Africa than to the Italian mainland.
Our correspondent says the reception centre there is full to bursting and residents are protesting as they fear that the immigrants will scare off tourists.
The second sea tragedy comes as Italy adopts new, tougher measures to turn back boat loads of immigrants.
The surge in the number of boats, often barely seaworthy and dangerously overloaded, has prompted a crisis within the Italian Government coalition, our correspondent says.
The Northern League is insisting on a tougher line, but suggestions that force be used to turn back the boats of immigrant smugglers have been dismissed outright by other ruling parties, our correspondent adds.