Afghan President Hamid Karzai came in for stinging criticism after accusing foreign powers of orchestrating enormous fraud in elections that returned him to power last year.

Karzai's outburst Thursday, just days after a fence-mending trip to Kabul by US President Barack Obama, met with disapproval in Washington while a former UN envoy said he was divorced from reality.

"There was fraud in presidential and provincial council elections -- no doubt that there was a very widespread fraud, very widespread," Karzai told Afghan election commission workers in Kabul.

"But Afghans did not do this fraud. The foreigners did this fraud," he said.

Karzai's once-close relationship with the United States and other allies, whose troops are helping his government contain a raging Taliban insurgency, has soured over his controversial re-election.

The United States brushed aside the accusations and insisted the Afghan leader first had to get his own house in order, after Obama Sunday called personally on Karzai to get a grip on widespread corruption.

"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," State Department spokesman Philip Crowley said.

White House spokesman Bill Burton said that despite some progress on cleaning up Afghanistan's notoriously graft-prone politics, "there is obviously a lot more work to do and we are going to continue to do it".

He said that Obama "and this government have made clear there are issues with governance in that country that can certainly be improved".

Using strong language, Karzai at one point accused former UN deputy head of mission Peter Galbraith of threatening a senior election official with harsh consequences if he announced electoral results in Karzai's favour.

"You'll be digging your grave by your own hands, should you announce the results," Karzai quoted Galbraith as telling chief electoral officer Daud Ali Najafi.

Galbraith was sacked after arguing the world body was turning a blind eye to the electoral chicanery. At the time, he said that as much as 30 percent of the Karzai vote in the August election was fraudulent.

Karzai was declared re-elected in November by his own officials after his challenger Abdullah Abdullah abandoned a run-off.

Interviewed by AFP, Galbraith said that at first he thought Karzai's comments were an April Fool's Day joke.

"It's obviously absurd and preposterous. It just underscores how unreliable Karzai is as an ally," he said. "Frankly, one questions if it's his emotional state or if he has a slim connection to reality.

"The important thing is that he has admitted he is in office by virtue of fraud. But it was obviously done by Afghans and the very people he appointed."

The remarks showed that Karzai was not taking Obama's warnings seriously and that "could make the military mission even more difficult", Galbraith added, warning that Afghanistan could descend into new conflict.

More than 126,000 US and allied troops are stationed in Afghanistan in a bid to quell the bloody Taliban revolt, and Obama is surging thousands more troops into a war that is now in its ninth year.

At the heart of the new US strategy is an emphasis on bringing good government to Afghans ground down by years of conflict, Taliban intimidation, rule by warlords and the pernicious influence of the opium trade.

Karzai's outburst came a day after a rare rebuke from Afghan lawmakers who voted against his amendments to a law banning non-Afghans from the UN-backed watchdog that was integral to exposing last year's fraud.

The Afghan president on Thursday criticised the parliament vote and defended his move to "Afghanise" the electoral process.

He also singled out the head of the EU election observer mission to Afghanistan, Philippe Morillon, for criticism. The mission had branded 1.5 million votes cast in the election as "suspicious".

Karzai accused "some embassies" -- which he did not identify -- of seeking to bribe electoral commission members by offering them armoured vehicles.

Spokesmen for the EU and UN missions in Kabul said they had no comment on Karzai's allegations.