More than 2,000 migrants and refugees have died so far this year in attempts to reach Europe by boat. (File photo)
A boat packed with up to 700 African migrants capsized in the Mediterranean Sea off the coast of Libya today and many are feared dead, officials and aid agencies said.
Italian Coast Guard spokesman Filippo Marini said first reports indicated there were between 400 and 600 people on board and that 25 bodies had been recovered so far.
The operation, which also included Italian and Irish vessels, was continuing, he added.
The humanitarian group Medecins sans Frontieres, whose rescue ship Dignity 1 was in the area, said in a tweet that the boat was believed to have been carrying about 700 people.
"The team on the Dignity 1 can confirm that there have tragically been many deaths but does not have figures at this stage," one of its tweets said.
In another tweet, the UN refugee agency UNHCR said about 600 people had been on board and that about 250 had been rescued.
Irish Defence Minister Simon Coveney said in a statement he feared that "loss of life is likely to be significant".
The Mediterranean Sea is the world's most deadly border area for migrants. More than 2,000 migrants and refugees have died so far this year in attempts to reach Europe by boat, compared with 3,279 deaths during the whole of last year, the International Organization for Migration said on Tuesday.
In April, a fishing boat with up to 800 migrants sank, making it the deadliest shipwreck in the Mediterranean for decades and a symbol of Europe's long-running migrant crisis.
The 20-metre (66-foot) vessel capsized as it approached a merchant ship that had come to its assistance.
© Thomson Reuters 2015