Valletta, Malta/Rome  - The sighting of seven bodies floating in Libyan waters by the European Union's border patrol agency this week increased concerns Friday over another possible tragedy at sea involving would-be immigrants.

A German helicopter forming part of the EU's Frontex mission, spotted one corpse on Tuesday, and six on Thursday, military officials in Malta said.

The announcement came after five Eritreans who were picked up at sea by the Italian coastguard earlier on Thursday, claimed they were the only survivors of a group of several dozen immigrants who left Libya 20 days ago.

The Eritreans - including one woman and two minors - were found in "precarious" health conditions, floating on a rubber dinghy after they had run out of food and water supplies. Italian officials said.

With the aid of interpreters the five have indicated that at least 73 of their fellow travellers died at sea, the bodies thrown overboard.

They also said that several vessels who passed close to their dinghy made no attempt to rescue them.

Italian Interior Minister Roberto Maroni said the claims needed to be verified, and has asked judicial authorities in Agrigento, Sicily to investigate the incident.

But several Italian opposition leaders and other critics said the deaths represented the failure of conservative Prime Minister Silvio Berlusconi's hard-line stance against illegal immigration.

"It is alarming that for over 20 days these people were floating around the Mediterranean but received no help from any passing vessel," United Nations Refugee Agency spokeswoman, Laura Boldrini, said.

Boldrini and other UN officials have criticised a recent Italian-Libyan accord aimed at curbing illegal immigration across the Mediterranean, a move which they say violates the rights of political refugees seeking asylum.

Italy and Malta have reported a drastic reduction in the number of would-be immigrants landing on their shores from Africa following the coming into effect earlier this year of the Rome-Tripoli pact.

Through the agreement, Libya has committed to stepping up patrols along its shoreline, which is often used by the mostly African migrants as a springboard to reach Europe.

Italy also began deporting to Libya would-be immigrants intercepted in international waters. (dpa)