Hundreds of refugees are feared to have died off the coast of Libya after five bodies were found near two capsized boats, while the search goes on for a third vessel.

Spanish aid organisation Proactiva Open Arms said its vessel was heading north to the Italian port of Catania to hand over the bodies of five young men found on Thursday.

Spokeswoman Laura Lanuza said other NGOs are continuing the search for more victims off the coast of Libya.

The UN refugee agency said it was "deeply alarmed" by the reports, and warned the death toll may be much higher as migrant dinghies are normally crammed with scores of people.

The UNHCR cited NGO sources saying the five bodies were recovered about 14 miles off the Libyan coast near two empty and partially submerged rubber dinghies.

Ms Lanuza said the boats were found north of the Libyan town of Sabratha. The five men, of African origin, were estimated to be aged between 16 and 25 and appeared to have drowned, she said.

The Red Crescent in Libya and the Libyan coastguard said they had no reports about dead migrants or capsized boats in the 12 miles of Libyan territorial waters.

The UNHCR said the latest incidents come after an intense week of arrivals through the central Mediterranean route with almost 6,000 migrants and refugees rescued in five days this week.

It said 21,903 people have crossed the Mediterranean Sea to European shores so far this year.

The agency said that since the beginning of 2017, and excluding the latest incidents, around 590 people have died or gone missing.

Last year was the deadliest recorded, with 5,096 migrants dying or going missing, according to the UNHCR.