Talks address migrant boats crisis
European leaders have arranged summit talks to address the migrant boat crisis as authorities tackled fresh emergencies in the Mediterranean.
David Cameron announced he will break off from election campaigning to attend a meeting of the European Council in Brussels.
It came as Italian and Maltese ships responded to distress calls from two boats with hundreds of people on board. In another incident, at least three people are believed to have died after a boat carrying migrants ran aground off the coast of the Greek island of Rhodes.
The latest reports came as rescue teams continued searching for bodies and survivors after up to 900 people were feared to have drowned off the coast of Libya at the weekend in the worst disaster of the emergency so far.
Shocking details of the incident - described by Mr Cameron as "a dark day for Europe" - have begun to emerge.
Many children are said to have been on board and there are claims that hundreds of migrants were locked in a hold by people smugglers.
It is thought the 20-metre (66ft) vessel capsized after migrants rushed to one side when they saw a passing Portuguese merchant ship approaching.
Gemma Parkin, of Save the Children, said 28 survivors of the shipwreck are being brought to Sicily.
Speaking from Catania, on the east coast of the island, she said no women or children are believed to have survived.
"There is a huge number of people presumed dead now," she told the Press Association.
Calling for an emergency summit, she said: "Whatever you think of migration, you can't let children drown in this way."
Earlier, the Prime Minister blamed trafficking gangs as pressure mounted to resume full-scale search and rescue missions.
He said: "It is a very dark day for Europe, it really is horrific the scenes that we have all witnessed on our television screens, the loss of life.
"We should put the blame squarely with the criminal human traffickers who are the ones managing, promoting and selling this trade, this trade in human life. We are doing everything we can to try and stop them.
"I believe what is necessary is a comprehensive approach.
"You have got to deal with the instability in the countries concerned, you have got to go after the human traffickers and the criminals that are running this trade.
"You have got to make sure, yes there is an element of search and rescue, but that can only be one part of this.
"We must use all the resources we have including Britain's aid budget, which can play a role in trying to stabilise countries and trying to stop people from trafficking."
The rising death toll comes as thousands of desperate migrants attempt to cross from North Africa to Europe, often crammed into unsafe boats.
Up to 1,500 have drowned this year alone and the Italian Navy and coastguard brought more than 13,000 people ashore in the space of just a week.
An Italian scheme called Mare Nostrum was abandoned late last year despite rescuing tens of thousands of people making the treacherous journey and was replaced with a more limited EU border security operation.
The latest developments have prompted renewed calls for the previous operation to be restored.
The UK had argued search and rescue operations might encourage more illegal immigrants.
Refugee Action chief executive Stephen Hale said: "Britain and other European countries must all play their part. We are in the midst of a global refugee crisis. Lives are at stake. Today, Europe's foreign ministers must rediscover their humanity, and restart search and rescue efforts."
Dr Ruben Andersson, a researcher at the London School of Economics and Political Science (LSE), said: "These man-made tragedies show that Europe's callous deterrence policies have failed in a terribly predictable manner.
"Last year EU member states, such as the UK, were warned that withdrawing rescue capabilities would have disastrous consequences. They chose to ignore these warnings."
Labour leader Ed Miliband told the BBC it was "wrong" to end search and rescue in the Mediterranean and called for the programme to be restarted.
"We have always had a proud tradition in Britain of looking after people in the most extreme circumstances, and these are the most extreme circumstances," he said.
Deputy Prime Minister Nick Clegg called for a "completely different strategy".
He rejected Nigel Farage's claim that Mr Cameron and Nicolas Sarkozy's "fanaticism" in bombing Libya directly caused the problem of migrant tragedies at sea, accusing him of "taking election-time political point-scoring to a new low".
Save the Children chief executive Justin Forsyth said: "What we needed from EU foreign ministers today was life-saving action, but they dithered. The emergency summit on Thursday is now a matter of life and death.
"With each day we delay, we lose more innocent lives and Europe slips further into an immoral abyss. Right now, people desperately seeking a better life are drowning in politics. We have to restart the rescue - and now."
Home Secretary Theresa May said: "We came together today urgently to look at what Europe's response should be to the tragic events in the Mediterranean ahead of the European Council meeting that will be taking place on Thursday. And the UK will consider what more we can do with our European partners.
"We have agreed to look to enhance the existing Frontex operation in the Mediterranean, which Britain already supports, but we all agreed that there are no quick fixes and the Frontex work can only be part of a wider approach to tackling illegal migration.
"We agreed that we need to look at every stage of the problem and crucially, and the key point, that we need to step up a gear in terms of dealing with the human traffickers and their ships.
"And we will be looking at enhanced co-operation between law enforcement agencies, we will be looking at how we can work better with third countries to ensure these journeys don't start, don't happen in the first place and also at how we can more effectively return illegal migrants."