At least 160 migrants have died in the space of a week after trying to cross the Mediterranean Sea from Libya.
Rescuers said two boats had capsized on consecutive days, with women and children among the dead and bodies starting to wash up on the coast.
A separate search and rescue mission was under way off the Greek island of Folegandros after a dinghy sank, killing at least one person.
Greek coastguards said they had rescued 12 people, including children, but there were conflicting reports about how many people had been on the boat.
The shipwrecks off Libya bring the death toll on the perilous route from North Africa to Europe to 1,500 this year, said the International Organisation for Migration.
Another 450 migrants were intercepted at sea and returned to the Libyan coast in the week ending on December 18.
Josep Borrell, the EU’s foreign policy chief, said he was saddened by the 163 reported deaths.
“We can and must do more to ensure a proper management of migration and prevent traffickers from putting people’s lives at risk through perilous journeys across the sea,” he said.
Capt Carola Rackete, one of the Mediterranean’s most prominent rescue ship captains, said refugee deaths should not be regarded as “simple accidents”.
The EU’s migration policy, the actions of Libyan authorities and a global reluctance to settle people through the UN were all to blame, she said.
Inspectors commissioned by the UN said in October that the treatment of migrants in Libya could amount to crimes against humanity.
The IOM said there were 102 people dead or missing, including 17 women and children, after the first wooden boat went down in the Mediterranean on Friday. It had left Sabratha, Libya, one day earlier.
The victims included people from Cameroon, Ghana, Nigeria, Mali, Cote d’Ivoire, Guinea, Senegal and Togo.
Another 61 people were missing or presumed drowned, their nationalities not given, in the second disaster a day later. The same day, another 210 people were taken back to Libya aboard a third wooden boat.
Late on Tuesday, the charity Doctors without Borders (MSF) said it had rescued another 69 people from a rubber boat.
When they were taken aboard the rescue ship Geo Barents, many were found to have leg injuries apparently inflicted deliberately.
Libya is a common departure point for migrants seeking to reach Europe, many of whom come from other North African countries, such as Tunisia and Egypt.
Arrivals across the Mediterranean in Italy have almost doubled this year.
Of those who arrived in Italy last month, the majority had started their journey in Libya, according to UN documents.
Others, who tried to make the crossing by land, have died in the Poland-Belarus border stand-off.
UN investigators said on Tuesday they had been denied access to inspect what they said were “dire conditions” on the Belarusian border.