The International Committee of the Red Cross (ICRC) has publicly denounced what it says are major human rights abuses by Burma's military government.
Government forces are accused of targeting border villages
In a highly unusual departure from its normally neutral stance, the ICRC said the actions of Burmese authorities were causing immense suffering to thousands.
The group accuses the regime of using detainees as army porters, and abusing people living along the Thai border.
It says Burmese officials have refused to discuss the abuse, or take action.
This statement is the harshest public criticism from the Swiss-based ICRC since it denounced the genocide in Rwanda more than a decade ago, the BBC's Imogen Foulkes in Geneva says.
It is a sign that the organisation, which prides itself on the results it can achieve in confidential discussions with governments, thinks there is little to hope for from Burma's military rulers, our correspondent adds.
The criticisms came as the US and Burma (Myanmar) held their highest-level meeting since 2003.
Deputy Assistant Secretary of State Eric John met three Burmese ministers and pressed for the release of democracy activist Aung San Suu Kyi, who has been under long-term house arrest, Washington said.
The actions of Burma's military government had "resulted in immense suffering for thousands of people in conflict-affected areas", ICRC President Jakob Kellenberger said in the strongly-worded statement.
Thousands of prisoners are being forced to work as porters for the armed forces - depriving them of food, and in some cases, killing them - the agency said.
And communities living along Burma's border with Thailand - where the military is fighting ethnic rebels - are being deliberately targeted by troops, the statement said.
Soldiers are accused of destroying food stocks, making arbitrary arrests and, again, in some cases killing civilians, forcing thousands to flee their villages.
All of these things, the ICRC said, have been witnessed by its staff, or documented by them in private interviews with civilians.
"Despite repeated entreaties by the ICRC, the authorities have consistently refused to enter into a serious discussion of these abuses with a view to putting a stop to them," Mr Kellenberger said.
"The continuing deadlock... has led the ICRC to take the exceptional step of making its concerns public."
Last October several ICRC offices were closed by the Burmese authorities, and ICRC delegates were forbidden to make prison visits.