Amos Wako said he had in no way obstructed or stifled reforms
Kenya's attorney general has threatened legal action against the US, after Washington imposed a travel ban on him.
Amos Wako admitted for the first time he was the unnamed official who was banned and accused the US of acting against him for "defamatory reasons".
There has been much speculation in Kenya about who was the subject of the US ban, announced last month.
The US said a number of officials were deliberately blocking political reforms following post-poll violence last year.
Some 1,300 people died in post-election clashes.
The US has urged Nairobi to clean up its act in order to avoid a repeat of the unrest after the next election.
'Man of many lives'
In a news conference Mr Wako strongly defended his position.
"The attorney general has not in any way obstructed or stifled reforms," he said.
"To target only the attorney general is therefore an American or foreign agenda."
The BBC's Josphat Makori, in the capital Nairobi, says Mr Wako is a man of many lives who has survived in his job despite years of criticism and civil society groups calling for his removal.
In his 15 years in power Kenya has seen its biggest financial scandal - and Mr Wako was widely derided for failing to bring a major prosecution, our reporter says.
And he shows no sign of stepping down now, telling reporters that he had no desire to go to the US, so the ban would not affect him.
Last month US officials announced they had banned a senior official from travelling, but declined to name Mr Wako.
They said the individual had "obstructed the reform process, failed to end the cycle of impunity and has been an obstacle in the fight against corruption".
The US has also sent letters to several other officials warning them they face travel bans if they failed to support the "reform agenda".
A power-sharing government was eventually set up after weeks of violence following the December 2007 election, but it has struggled to restore stability.
Rights groups blamed the police for many of the deaths in the riots.
International mediators have pressed the government to set up a tribunal to investigate the killings, but officials have missed every deadline they have been set.
In July, former UN chief Kofi Annan passed the names of those accused of orchestrating the violence to the International Criminal Court (ICC) in a sealed envelope.
The list, drawn up by a Kenyan judicial commission, has not been made public.
The ICC has said it will prosecute them and the ICC's chief prosecutor Luis Moreno-Ocampo is expected in Nairobi on Thursday.