Mrs Clinton said Kenya had been pulled "from the brink of distaster"
US Secretary of State Hillary Clinton has described as disappointing Kenya's failure to investigate a bout of deadly violence after the 2007 election.
Speaking in Nairobi on the first day of her African tour, Mrs Clinton urged the Kenyan authorities to end impunity.
At least 1,300 people were killed in two months of violence, but the cabinet has resisted calls for a tribunal.
Earlier, Mrs Clinton told a trade summit that Africa needed democracy to help boost its economic performance.
Addressing the press following a meeting with the Kenya's president and prime minister, Mrs Clinton strongly criticised Kenya's political leadership.
She said the absence of strong and effective institutions had permitted ongoing corruption, impunity and human rights violations.
And she noted that these conditions had helped fuel the violence that engulfed the country in early 2008.
"We've been very clear in our disappointment that action has not been taken [over the violence]," she said.
"It is far preferable that it be done in the regular course of business, that prosecutors, judges, law enforcement officials step up to their responsibilities and remove the question of impunity."
The violence broke out after supporters of Raila Odinga - the main opposition leader at the time - said he had been cheated of victory in the December 2007 polls.
The crisis ignited long-standing ethnic rivalries over access to land and other economic resources, and some 300,000 people were forced to flee their homes.
After two months of violence, a deal was brokered which saw Mr Odinga joining a power-sharing government as prime minister with President Mwai Kibaki.
The Kenyan cabinet recently decided against setting up a special tribunal to try the perpetrators of the violence.
The BBC's Will Ross, in Nairobi, says several senior politicians have been accused of fuelling the fighting - so the move was widely seen as a means of protecting themselves from justice.
Democratic Republic of Congo
However, Kenyan Foreign Minister Moses Wetangula rejected the accusations, saying: "The war against impunity in the country is on, that the war against corruption is on."
Earlier Mrs Clinton addressed African leaders at an economic summit and told them the continent had "enormous potential for progress".
But she stressed that harnessing that potential would require democracy and good governance.
Later in the week she is expected to meet Sheik Sharif Sheik Ahmed, the president of Somalia's beleaguered UN-back government.
Officials say she is likely to pledge more military and financial backing for the government, which is beset by insurgencies from several Islamist militant groups.
During her 11-day trip Mrs Clinton will also visit South Africa, Nigeria, Angola, Liberia, the Democratic Republic of Congo and Cape Verde.