Burma is expelling the top UN diplomat in the country, UN officials have said.
Burma's military violently suppressed September's protests
The military regime told UN Burma country chief, Charles Petrie, his mandate was not being renewed.
The news comes a day before UN special envoy Ibrahim Gambari is to return to Burma for a second visit since the army suppressed anti-government protests.
The US said the expulsion of Mr Petrie, who has criticised the violent suppression of the protests, was an insult and an outrage.
It is not clear when Mr Petrie, who began his posting in Burma in 2003, will have to leave the country.
But the timing of the junta's decision, one day before Mr Gambari's visit begins, is dramatic, says the BBC's James Reynolds in the Thai capital, Bangkok.
It makes his trip, one that was already looking difficult, much more difficult, says our correspondent.
On 24 October, United Nations Day, Mr Petrie issued a statement critical of the country's deepening economic crisis.
A sharp rise in fuel prices triggered protests in mid-August that snowballed into mass pro-democracy demonstrations led by thousands of Burmese monks.
"The events clearly demonstrated the everyday struggle to meet basic needs and the urgent necessity to address the deteriorating humanitarian situation in the country," Mr Petrie's statement said.
Mr Petrie has also spoken out about the Burmese crackdown on September's mass protests.
White House spokesman Gordon Johndroe said the expulsion was an attempt by the junta "to hide their atrocities from the world".
"This outrageous action the day before the arrival of [Mr] Gambari in Burma is an insult to the United Nations and the international community," he said.