Around 150 people are feared drowned following a shipwreck off the coast of Libya, the UN says.
The UN refugee agency (UNHCR) said it happened off the coast of Al Khoms.
Two boats carrying about 300 people capsized around 120km east of the capital, Tripoli.
It said another 147 people have been rescued but many others may have lost their lives.
Charlie Yaxley, spokesman for the UN refugee agency, said: "We estimate that 150 migrants are potentially missing and died at sea."
UN refugee chief Filippo Grandi said it is the worst tragedy in the Mediterranean this year.
The worst Mediterranean tragedy of this year has just occurred. Restoring rescue at sea, ending refugee+migrant detention in Libya, increasing safe pathways out of Libya must happen NOW, before it is too late for many more desperate people. https://t.co/XuZJpDtZfv
— Filippo Grandi (@FilippoGrandi) July 25, 2019
Medecins Sans Frontieres said it was assisting 135 survivors from the wreck and said eye witnesses had seen at least 70 bodies in the water.
It said the patients are in shock and had come close to drowning. Seven people have been referred to hospital for life saving treatment.
Over 100 people are missing, many feared drowned in the shipwreck. #MSF medical teams stabilized survivors with most urgent needs and referred 7 people for life-saving hospital treatment.
Patients are in shock and suffer from their nearly drowning
— MSF Sea (@MSF_Sea) July 25, 2019
Last Sunday, the charity resumed its search and rescue operations in the Mediterranean and condemned EU governments for their failure to do so.
It said its return to sea came after a sustained two-year campaign by EU governments to stop virtually all humanitarian action at sea, and the normalisation of vindictive policies that have caused deaths at sea and suffering in conflict-ridden Libya
MSF Head of Mission for Search and Rescue Sam Turner said: “Politicians would have you believe that the deaths of hundreds of people at sea, and the suffering of thousands of refugees and migrants trapped in Libya, are the acceptable price of attempts to control migration.”
“The cold reality is that while they herald the end of the so-called European migration crisis, they are knowingly turning a blind eye to the humanitarian crisis these policies perpetuate in Libya and at sea.
“These deaths and suffering are preventable, and as long as it continues, we refuse to sit idle.”
It came after the UN called on the EU to resume naval patrols in the area and said the patrols saved “thousands of lives” in the past.
Around 2,275 people died or went missing while attempting to cross the Mediterranean in 2018, UNHCR figures show.
UN officials have called for urgent international action to address the crisis, including ending the arbitrary detention of refugees and migrants in Libya.
In the wake of a number of countries taking action against rescue vessels, UNHCR has also said NGOs should 'not be criminalised nor stigmatised' for saving lives at sea.