The special envoy of the UNHCR for the Central Mediterranean has slammed the inaction of Mediterranean states after migrants died on a boat which drifted at sea for days.

'This boat should never have been left drifting," Vincent Cochetel wrote in a tweet.

"Loss of lives could have been avoided. Those considering Libya a safe port should visit the survivors in the awful detention centre where they are. No one can honestly ignore today what “rescue” by the Libyan Coast Guard leads to."

Five migrants were found dead in the boat when some 50 survivors were rescued by a cargo ship. The survivors said another seven people were missing, presumed dead.

The survivors were later transferred to a Libyan boat, which took them back to Libya. They have since been arrested and taken to a detention camp.

Italy and Malta have declared their harbours closed to migrant disembarkations, citing COVID-19 pressures on resources.

Malta has defended its actions regarding the boat, saying that it had been in distress for a number of days while in Libya’s search and rescue area before moving closer to Malta.

"The European Union was aware of the boat in Libya’s SAR and although it flew its aircraft over the area, it did not send any vessels to pick up the migrants," it said.

Once the boat was in Malta's rescue zone, the Maltese armed forces called nearby vessels to assist.  

The UNHCR insisted in a separate tweet, however, that Libya is a country at war and not a safe port for refugees and asylum-seekers to be returned to.