By Carl Odera
JUBA (Reuters) - Three crew members of a U.N. peacekeeping helicopter in South Sudan were killed on Tuesday when their aircraft crashed on a routine cargo flight, the United Nations said.
A fourth crew member of the Mi-8 helicopter contracted to the U.N. Mission in South Sudan (UNMISS) was being treated for injuries after the crash near Bentiu, the capital of oil-producing Unity State which lies in the north of the country.
The U.N. mission was launching an investigation to determine the cause of the crash, Toby Lanzer, the officer-in-charge of UNMISS, said in a statement.
The U.N force, set up after South Sudan's independence in 2011, has been seeking to protect civilians after a conflict erupted in December that pits troops loyal to President Salva Kiir against those supporting his rival Riek Machar.
At least 10,000 people have been killed in fighting which has rumbled on despite ceasefire deals agreed between the two sides during peace several months of peace talks in Ethiopia.
Initially set up to protect civilians as well as carry out other state building work, the U.N. Security Council in May authorized the peacekeepers to focus on protecting civilians and backed the use of force.
UNMISS has an approved strength of up to 12,500 military personnel and more than 1,300 civilian police personnel.
(Additional reporting by Louis Charbonneau in New York; Writing by Edmund Blair; Editing by Alison Williams and Susan Fenton)