The United Nations refugee agency says the Mediterranean Sea is the deadliest stretch of water for migrants and refugees seeking to escape poverty and oppression.

In a new report, U.N. officials estimate that 1,500 people died last year while trying to cross the sea from Africa to Europe. They say this is just an estimate, and that the actual number of deaths may be higher.

Officials say people trying to escape the turmoil in such countries as Libya and Tunisia in 2011 accounted for the high death toll. Most of the migrants tried to reach Malta and the Italian islands — the closest European Union territory to northern Africa.

Those who survived the dangerous journey described armed guards forcing them to climb aboard unsafe boats, and abuse and torture at sea by other passengers.

U.N. officials urge all ships' captains in the Mediterranean to stay vigilant and rescue all those in distress.