The UN Security Council has voted to refer war crimes suspects in Sudan's Darfur region to the International Criminal Court (ICC).
At least 100,000 people are thought to have died in Darfur
Washington had received assurances that no US members of any peacekeeping operation in Sudan would be prosecuted.
A UN report two months ago said attacks on civilians in Darfur could amount to crimes against humanity.
A Darfur rebel leader says he will hand himself to the court, if he is charged, while Sudan has criticised the vote.
"It is definitely a breakthrough," said analyst David Mozersky from the International Crisis Group think-tank.
"It's too early to talk about an end to the war, but it is the first time that we have a formal measure of international accountability for what has gone on in Darfur."
The UN says that some 180,000 people have died in the two-year conflict.
Pro-government Arab militias are accused of widespread atrocities, including mass rape and killings and looting.
The Sudan government denies charges that it armed the Janjaweed militias.
Continuing insecurity with attacks on drivers is hampering attempts to deliver food aid to some 2m displaced people in Darfur, the UN says.
"These attacks create a climate of fear. The security situation is so bad that many drivers are refusing to move through sections of the roads," the UN World Food Programme's Ramiro Lopes da Silva said.
The UN report said war crimes suspects should be tried at the court in The Hague.
After weeks of negotiations, the US finally withdrew the threat to veto the resolution referring those accused of committing atrocities in Darfur to the ICC.
Instead, the US - as well as with China, Algeria and Brazil - decided to abstain on the resolution, which was passed 11-4.
Washington has consistently opposed the ICC on the grounds it could be used for politically-motivated prosecutions.
In a concession to the US, the UN resolution stated that peacekeepers and civilians of countries which have not ratified the court and who are working in Sudan could only be tried at home if accused of a crime.
This exception was criticised as "totally unacceptable" by human rights group Amnesty International.
"It creates double standards of justice," said Amnesty's Yvonne Terlingen, saying it should be excluded from all future Security Council resolutions.
Sudan also criticised the vote, saying it was unfair and Sudan's courts were able to try those accused.
"Justice here is a great good used in the service of evil," said Sudan's UN ambassador Elfatih Mohammed Erwa after the vote.
But it was welcomed by the leader of one of the Darfur rebel groups, the Sudan Liberation Army.
"I myself personally if my name is on that list or any other member of our movement we are ready to go because we are just fighting for justice," said Abdel Wahed Mohamed al-Nur.
The US deputy ambassador to the UN, Anne Patterson, said they felt they had full protection for Americans in the resolution.
Last week the Security Council passed a resolution to impose sanctions on anyone who tries to impede the peace process in Darfur.