By Hereward Holland
JUBA (Reuters) - The United Nations peacekeeping force in South Sudan lacks sufficient troops and aircraft to protect civilians affected by fighting in an eastern region, the U.N. envoy said on Monday.
Tens of thousands of people have been uprooted by clashes between the army and rebel forces in Jonglei state.
Almost all of the 10,000 residents of Pibor town in Jonglei have fled their homes, aid agencies say, following looting by the state security forces and rebel threats to attack it.
The head of the U.N. mission, Hilde Johnson, said she has doubled the number of peacekeeping troops in Pibor.
"We cannot sustain a presence with the logistical capacity that we have, with the problems we have with air transport and by road. So we cannot protect civilians in big, big, big numbers," Johnson told Reuters.
The U.N. mission has 6,560 troops to cover a country the size of France with barely 300 km (200 miles) of paved roads.
Seasonal rains have turned the region, where the government hopes to drill for oil with France's Total, into a swamp, severing road access.
On April 9, gunmen ambushed and killed five U.N. peacekeepers and seven civilian staff in Jonglei.
Earlier this month President Salva Kiir said he would punish ill-disciplined members of the security forces engaged in acts of violence against civilians in Jonglei and also those who gave the orders.
Johnson also dismissed criticism by a Dutch think-tank, the Clingendael Institute, which said the U.N. mission steered clear of confrontation with the government and failed to fulfill its role as a watchdog.
"If you come as an outsider with no history, and you come waving the whip, I can assure you that the outcome is not necessarily going to be the most positive one for your cause," the Norwegian envoy said.