The United Nations on Thursday appealed to donors for $71.4 million to respond to the needs of some 250,000 people impacted by the floods in Libya over the next three months, saying death tolls could rise without more help.

"There is a heightened concern regarding the potential rise in morbidity and mortality rates if immediate and adequate aid is not dispatched to the affected regions," the U.N. document said. The appeal targets only about a quarter of the 884,000 people it said have been directly affected by the floods.

It said satellite analysis indicated that 2,200 buildings have been hit by flooding in the worst-affected city of Derna and described the situation in the submerged city of Sousse as "critical".

(Reporting by Emma Farge Editing by Miranda Murray)