At least 40 Europe-bound refugees were missing and feared drowned after the boat they were travelling in capsized in the Mediterranean Sea off Libya, the coast guard and the UN refugee agency said.

Ayoub Gassim, a spokesman for Libya's coast guard, said at least five bodies, including a child, were recovered near the western town of Khoms, around 75 miles east of Tripoli.

He said they rescued at least 65 migrants, mostly from Sudan, and that search operations are under way for those still missing.

Charlie Yaxley, a spokesman for the UN refugee agency, said at least 40 people are estimated to be dead or missing.

Alarm Phone, an independent support group for people crossing the Mediterranean, said up to 100 migrants were on board the capsized vessel.

In pictures: A day of refugee rescues in the Mediterranean Sea Show all 7 1 /7 In pictures: A day of refugee rescues in the Mediterranean Sea In pictures: A day of refugee rescues in the Mediterranean Sea A baby being taken on to MSF's Bourbon Argos ship from a boat carrying 130 migrants and refugees Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A refugee boat carrying 101 people being rescued by MSF's Bourbon Argos Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A refugee boat carrying 101 people being rescued by MSF's Bourbon Argos all images by Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A baby among refugees on a boat carrying 185 people off the coast of Libya Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea Migrants and refugees sleeping after being rescued by MSF's Bourbon Argos ship Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A crew from MSF's Bourbon Argos ship rescuing a boat carrying 130 migrants and refugees off the coast of Libya, at sunrise Lizzie Dearden In pictures: A day of refugee rescues in the Mediterranean Sea A woman in a stretcher being lifted onto MSF's Bourbon Argos ship from a boat carrying 130 migrants and refugees off the coast of Libya Lizzie Dearden

The group said it received a call from migrants on the boat, who "were in severe distress, crying and shouting, telling us that people had died already".

Libya's coast guard says it has intercepted hundreds of migrants at sea so far in August.

Libya became a major conduit for African migrants and refugees fleeing to Europe after the uprising that toppled and killed Muammar Gaddafi in 2011.

Traffickers and armed groups have exploited Libya's chaos since his overthrow.

In recent years, the European Union has partnered with the coast guard and other Libyan forces to prevent migrants from making the dangerous journey by sea to Europe.

Rights groups say those efforts have left migrants at the mercy of brutal armed groups or confined in squalid detention centres that lack adequate food and water.

At least 2,500 migrants are detained in centres in and around Tripoli, where forces loyal to Field Marshal Khalifa Hafter have been battling an array of militias loosely aligned with a UN-recognised government since April.

The government blamed the airstrike on the detention centre on Mr Hafter's forces, which denied responsibility and accused government-linked militias of storing weapons at the facility.

Refugee crisis: More than 500 migrants rescued in single day in Mediterranean Sea

The UN refugee agency says 164 migrants have died travelling from Libya to Europe this year, fewer than in previous years.

But the UN says the journey is becoming more dangerous for those who attempt it, with one out of four perishing at sea before reaching Europe.

The numbers did not include up to 150 Europe-bound migrants missing and feared drowned when their boats capsized in the Mediterranean Sea off Libya last month.