The death toll from Sunday's (19 April) disaster off the coast of Libya was uncertain but likely to be the highest in modern times among migrants trafficked in rickety boats across the Mediterranean, making April 2015 the worst month for loss of life in the Mediterranean, the United Nations' refugee agency UNHCR said on 20 April.

"As of right now, the reports remain there is about 700 people believed to have been aboard this boat, we are looking at whether this number might rise further as the accounts from survivors come in, but about 700, and at least I think several dozens people – up to 50 people – have been rescued. But nonetheless, it's a massive tragedy, what we are seeing, probably the biggest that's been recorded and it looks like it's making April of 2015 the worst month we have ever seen for losses of life on the Mediterranean," UNHCR spokesman Adrian Edwards said.

European Union foreign ministers met on Monday under pressure to produce more than words and save desperate migrants drowning in the Mediterranean, as bodies of the deadliest known wreck of its kind were brought ashore in Malta.

European officials are struggling to come up with a policy to respond more humanely to an exodus of migrants travelling by sea from Africa and Asia to Europe, without worsening the crisis by encouraging more to leave.

"Saving lives is the urgent need right now, it does need a robust response, we do need to see proper search and rescue on the Mediterranean, and we do need to look at what can be done to address these refugee flows at much earlier stages. So a comprehensive look at this involving many countries working together really is the only way we see forward," Edwards said.

An Italian naval operation in the southern Mediterranean, known as "Mare Nostrum", was cancelled last year because of its cost and domestic opposition to sea rescues that could encourage more migration.

It was replaced in November by a far smaller EU mission with a third of the budget, a decision that seems to have made the journey much deadlier for migrants packed into rickety vessels by traffickers who promise a better life in Europe.

"People fleeing in desperation aren't fleeing out of choice, they are fleeing because their lives depend on them finding safety, and in those circumstances, you are going to see more people crossing the Mediterranean, more people in need of international protection, in need of proper help," he said.

A wooden sailboat carrying dozens of immigrants also ran aground on Monday off the coast of the Greek island of Rhodes and at least three people have drowned, the Greek coast guard said.

More than 90 people were rescued and 30 of those taken to hospital. The boat was totally wrecked, the coast guard said.