The United States has rejected President Hamid Karzai's anti-foreigner outburst as "troubling" and "preposterous,” prompting a hurried effort by the Afghan leader to make amends.

Officials said Karzai did not specifically apologize during a telephone conversation with Secretary of State Hillary Clinton on Friday, but expressed "surprise" at the furore over his claim that foreigners orchestrated election fraud.

The row came just a few days after President Barack Obama made an unannounced trip to Kabul to press Karzai on tackling corruption and to demand progress on good governance, as Washington's troop surge strategy unfolds against the Taliban.

The new confrontation will only raise doubts about the fragile relationship between the Obama administration and Karzai, whom Washington is forced to consider a partner despite distaste for his political record.

Obama spokesman Robert Gibbs called Karzai's comments "troubling" and "cause for real and genuine concern."

Gibbs noted the huge US military and political resources — and sacrifices — committed to Afghanistan.

State Department spokesman Philip Crowley meanwhile described Karzai's intervention as "preposterous."

US ambassador to Kabul Karl Eikenberry also met with Karzai in person to seek clarification on his comments onThursday.

The Afghan leader then initiated the call to Hillary and expressed "surprise that his comments had created what he called a stir," a US official told AFP on condition of anonymity.

"Generally we were happy with the call and we're moving on," the official added.

Crowley called the conversation a "constructive" one as Washington and Kabul seek to defuse tense relations.

"President Karzai reaffirmed his commitment to the partnership between our two countries, and expressed his appreciation for the contributions and sacrifices of the international community," he said, adding that Karzai and Hillary "pledged to continue working together in a spirit of partnership."

But the Obama administration scrapped a planned Karzai visit to Washington last month after he gave himself full control over the electoral commission. In another snub to the United States, he then invited Iranian President Mahmoud Ahmadinejad to visit Afghanistan.

The Afghan leader drew fierce global condemnation for his speech on Thursday.