President Karzai's election was marred by fraud allegations
The Afghan president must set up a "major crimes tribunal" and an anti-corruption commission, US Secretary of State Hillary Clinton says.
She told ABC television that Hamid Karzai "can do better".
The Afghan leader - recently re-elected in a poll marred by fraud allegations - has come under growing Western pressure to deal with corruption.
One of Mr Karzai's spokesmen insisted the Afghan leader's administration was "serious" about tackling corruption.
The American ambassador in Kabul has warned against a US troop surge unless Mr Karzai takes action against corruption.
His views are at odds with US generals recommending a major troop deployment.
Afghanistan's chief prosecutor has said he has a list of senior officials and ministers suspected of taking bribes, but refused to publish their names.
Chief prosecutor Ishaq Aluko told the BBC last week that he had asked the president and Supreme Court to set up a special court to deal with the cases.
The presidential election in August was tainted with accusations of fraud and vote-rigging. Mr Karzai's main rival pulled out of a run-off vote.
Mrs Clinton, in an interview on ABC, said Washington expects "a major crimes tribunal" to be set up and "an anti-corruption commission established and functioning".
She said the Afghan government needed to take action against people who have "taken advantage of the money that has poured into Afghanistan" in the past eight years.
She said she had made it clear that civilian aid would not be given unless the US could track it if it went to government ministries.
Mrs Clinton said the goal of the US was to defeat al-Qaeda, and help Afghans defend themselves against the Taliban.
"Now we believe that President Karzai and his government can do better," she said.
"We've delivered that message. Now that the election is finally over, we're looking to see tangible evidence that the government, led by the president but going all the way down to the local level, will be more responsive to the needs of the people."
Corruption in Afghanistan - which is the world's largest producer of opium - is linked mainly to illegal drugs, according to the United Nations Office on Drugs and Crime.
It has also said the unprecedentedly large amount of international assistance, and pressure to spend resources quickly, also contribute to corruption.
Afghanistan is regularly listed as among the worst five countries - out of 180 - for corruption by watchdog groups.