At least 20 migrants are feared dead after another incident involving migrant boats off the Libyan coast, the International Organisation of Migration (IOM) said after receiving a distress call.
The IOM said a person on board one of three boats carrying hundreds of migrants made the call on Monday, a day after another boat sank in the same area.
The Switzerland-based organisation reported that the caller said a ship was sinking with 300 people on board.
Coastguards were trying to verify the call and location of the boat.
Earlier in the day, 83 people were rescued after a boat carrying migrants ran aground off the Greek island of Rhodes, police said.
Three deaths were confirmed by the Greek coastguards in that shipwreck.
The latest incident comes as EU foreign ministers are meeting in Luxembourg to discuss their response to the migrant emergency in the Mediterranean.
John Dalhuisen, Amnesty International's Europe and Central Asia director, called on European governments on Monday to prioritise setting up an immediate search and rescue plan to prevent the escalating death toll of migrants attempting to cross the Mediterranean Sea.
"EU and European leaders have repeatedly spoken of the need for a holistic approach to this crisis, working with countries of origin and transit, and clamping down on people smugglers," Dalhuisen said. "These are important, but the immediate priority must be the immediate safety of refugees and migrants who will continue to make the perilous journey across the Mediterranean to Europe."
"Ministers must emerge from today"s meeting with a collective European search and rescue proposal," he said.
Hundreds of migrants were thought to have drowned when their boat overturned on Sunday, off the coast of Libya.
Up to 1,500 migrants are now feared to have drowned this year alone.
Many European governments have long been reluctant to fund rescue operations in the area for fear of encouraging more people to make the crossing in search of a better life in Europe, but they now face outrage over the refugee deaths.
"Europe can do more and Europe must do more," said Martin Schulz, president of the European Parliament.
"It is a shame and a confession of failure how many countries run away from responsibility and how little money we provide for rescue missions."
William Lacy Swing, chief of the IOM, urged the European countries to support Italy's Mare Nostrum rescue operation, which was stopped last year due to high operating costs.
Mare Nostrum, created after more than 350 people drowned off Lampedusa in October 2013, rescued 130,000 people last year.
Italy scaled back Mare Nostrum after failing to persuade its European partners to help meet its operating costs of $12m a month.
Federica Mogherini, the EU foreign policy chief, said she was determined to build a "common sense of responsibility" to tackle the crisis and that EU leaders are considering an emergency summit in Brussels this week.
It is the European Union's "moral duty to concentrate our responsibility as Europeans to prevent these kind of tragedies from happening again and again," Mogherini said before the meeting in Luxembourg on Monday.
"We must build a common sense of European responsibility, knowing that there is no easy solution, no magic solution."
Source: Al Jazeera and agencies