GENEVA, April 20-- As many as 500 people may have lost their lives when a large ship went down in the Mediterranean Sea at an unknown location between Libya and Italy this weekend, the UN refugee agency UNHCR said on Wednesday.

In a press release, UNHCR said that if confirmed, this could be one of the worst tragedies involving refugees and migrants in the last 12 months.

UNHCR said that the information was based on interviews with a group of survivors, including 37 men, three women and a three-year-old child, who were rescued by a merchant ship and taken to Kalamata, in the Peloponnese peninsula of Greece on April 16.

Those rescued include 23 Somalis, 11 Ethiopians, 6 Egyptians and a Sudanese, UNHCR said.

"The survivors told us that they had been part of a group of between 100 and 200 people who departed last week from a locality near Tobruk in Libya on a 30-meter boat. After sailing for several hours, the smugglers in charge of the boat attempted to transfer the passengers to a larger ship carrying hundreds of people in terribly overcrowded conditions, and at one point during the transfer, the larger boat capsized and sank," the statement said.

According to the UN agency, the 41 survivors include people who had not yet boarded the larger vessel, as well as some who managed to swim back to the smaller boat.

"They drifted at sea possibly for three days before being spotted and rescued on April 16," UNHCR noted.

The UN agency visited the survivors at the local stadium of Kalamata where they have been temporarily housed by local authorities as they undergo police procedures.