Speaking to a gathering of election officials on Thursday, Karzai said: "Foreigners will make excuses, they do not want us to have a parliamentary election.
"You have gone through the kind of elections during which you were not only threatened with terror, you also faced massive interference from foreigners."
Karzai said that such interference meant that Afghans could begin to see the 126,000 foreign troops in the country as "invaders" and the Taliban as "a national resistance".
Al Jazeera David Chater, reporting from Kabul, said that the reaction in political and diplomatic circles was one of "open astonishment".
"But you have to give a bit of background to this. It is now very apparent that when [US President Barack] Obama came here last Sunday, he read the riot act to President Karzai over good governance and corruption.
"I think we are seeing the reverberations now of the deterioration in relations between the White House and Karzai here in Kabul."
The US dismissed Karzai's comments on Thursday, saying that he should get his own house in order before accusing others.
"Karzai has to step forward, lead his government in convincing the international community and the Afghan people that they are taking measurable steps to reduce corruption," PJ Crowley, the US state department spokesman, said.
Karzai is due to visit Washington on May 12 after Obama issued a personal invitation during last week's trip to Afghanistan.
Karzai singled out Peter Galbraith, then deputy head of the UN mission, who he said had organised the fraud and fed details to the international media in an attempt to blacken his name.
"This wasn't fraud by Afghans but the fraud of foreigners, the fraud of Galbraith, of [head of the EU's observers Philippe] Morillon and the votes of the Afghan nation were in the control of an embassy."
|Abdullah said he was concerned about Karzai's well-being after the remarks [File: Gallo/Getty]
Galbraith, a former US diplomat, was dismissed last year after alleging that the UN was not doing enough to combat fraud in the election.
Galbraith responded that the accusations against him were "extraordinary".
"When I heard them this morning, I thought it was an April Fool's joke, but then I realised I didn't have that kind of relationship with President Karzai," he told Al Jazeera from Rome.
"It was President Karzai and the people he appointed to Afghanistan's election commission that committed the fraud that got over one million phoney votes for Karzai.
Galbraith said it is an interesting admission on Karzai's part that "he now thinks there was a vast fraud, which is of course what I said right from election day.
"President Karzai seems to have a rather slim connection to reality, especially if he thinks anyone is going to believe these kind of charges, and it really underscores just how unreliable he is as an ally."
Karzai's international reputation took a battering when a UN-backed fraud watchdog threw out one-third of the votes cast for him in the presidential election.
He is now battling with the Afghan parliament and the UN over fraud-protection measures for a parliamentary vote due in September.
The lower house of parliament threw out on Wednesday a presidential decree revoking the power of the UN to appoint the majority of members of the election fraud watchdog.
The UN has called for reforms to Afghanistan's election commission to prevent fraud, before it will agree to free up donor funds needed to pay for the September 18 vote.