* U.N. says investigating cause of crash
* Russian airline company says helicopter likely shot down
* Crash site in oil conflict flashpoint area (Adds rebel comment in paragraphs 8-9)
By Carl Odera and Gabriela Baczynska
JUBA/MOSCOW, Aug 26 (Reuters) - A U.N. peacekeeping helicopter in South Sudan was shot down on Tuesday and three of its crew were killed, Russian airline UTair, which owns the aircraft, said, citing initial information.
The airline said the helicopter, carrying four crew members, had been shot down as it flew over an area that has been a flashpoint during a civil conflict that is now more than eight months old.
"According to preliminary information, the helicopter was shot down with surface-to-air fire," UTair said in a statement.
"One crew member - the second pilot - is alive and has been transported to a hospital ... with minor injuries. Other crew members - commander, flight engineer and flight attendant - were killed."
The United Nations confirmed three crew members had been killed and one was being treated for injuries, but it had no immediate comment on the Russian report that the helicopter, which was on a routine cargo flight, had been shot down.
The U.N. Mission in South Sudan (UNMISS) said an investigative team would arrive at the crash site on Wednesday.
A spokesman for the Russian embassy in Sudan, Artur Safukov, told Russia's state broadcaster Rossiya 24 that all four on board were Russian citizens.
The Mi-8 helicopter crashed about 10 km (6 miles) south of Bentiu, the capital of oil-producing Unity State, which lies in the north of the Africa's newest nation, UNMISS said.
Toby Lanzer, the officer-in-charge of UNMISS, and UTair both said the helicopter, which was contracted to the U.N. mission, had been flying from Wau in the southwest to Bentiu in the north.
UTair, which said it has been working with the United Nations since 1991, said it was temporarily halting flying over the area.
Fighting has often flared in Unity State as rivals battle to control vital oilfields. The conflict has pitted soldiers loyal to President Salva Kiir against troops backing the former deputy president, Riek Machar. Despite two ceasefire pacts, fighting has continued.
The rebel delegation at peace talks in Ethiopia issued a statement denying what it said was South Sudanese government accusations that rebel forces brought down the helicopter.
"The area in which the (aircraft) was reportedly shot down is government-held territory, if indeed the aircraft was shot down," the rebel statement said.
The U.N force, set up after South Sudan's independence in 2011, has been seeking to protect civilians. At least 10,000 people have been killed in the fighting, which has driven the nation to the brink of a "man-made" famine.
Peace talks in Ethiopia have made little significant progress. The United States and European Union have imposed sanctions on commanders from both sides and regional African states sponsoring negotiations have threatened punitive measures against those impeding talks, but to little avail.
Initially set up to protect civilians as well as carry out other state-building work, the UNMISS peacekeepers were authorised by the U.N. Security Council in May 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 and Aaron Maasho in Addis Ababa, Writing by Edmund Blair, Editing by Susan Fenton)
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