REUTERS--   More than 600,000 Rohingya have fled Buddhist-majority Myanmar since late August this year for neighbouring Bangladesh, driven out by a military clearance operation in Rakhine State.

The refugees' suffering has caused an international outcry, spurring appeals by aid agencies for millions of dollars in funds to tackle the crisis.

"I found this was a population that had almost no response. Very passive," said Filippo Grandi, the U.N. high commissioner for refugees, describing his visit late in September to camps where the refugees were staying.

"You almost felt there was nothing left and that everything had been drained by this," he told Reuters in an interview in his first visit to the South Korean capital.

He saw the lassitude as a symptom of trauma, he added.

"We haven't seen this kind of trauma for a very long, long time," the Italian diplomat said. "Maybe I saw it in the '90s in central Africa."

Grandi coordinated UN humanitarian activities in the Democratic Republic of Congo during its 1996-97 civil war.

The success of aid efforts by the United Nations and non-government bodies depends on the Myanmar government to defuse the hostility facing humanitarian workers in Rakhine, Grandi said.

"It's not political work, it's not to favour one community over the other," he said.

"On the contrary, it's directed to all those who are in need. And when members of the Buddhist community are in need, they certainly qualify for that. I think it's important that they stress that, they do that more," said Grandi.

Tension had been rising between the government and aid agencies even before the spasm of violence that began in late August.

Officials had accused the World Food Programme of aiding insurgents after high-energy biscuits were discovered in July at a forest encampment the authorities said belonged to a militant group, the Arakan Rohingya Salvation Army.