The United States and Afghan President Hamid Karzai traded fresh recriminations Monday after failing to put a lid on a row over election fraud which is tearing at their uneasy alliance.

Karzai reignited a controversy which is frustrating the White House in a reported meeting with Afghan lawmakers and refused to back down from claims that foreigners helped to rig Afghan elections in an interview with the BBC.

"The remarks are troubling and the substance of the remarks is simply not true," White House spokesman Robert Gibbs said, following the latest Karzai outbursts, just a week after President Barack Obama's surprise visit to Kabul.

Another senior US official, speaking on condition of anonymity, said Obama's administration was struggling to understand the motivation behind Karzai's recent comments.

"Up to a point, we understand that there are things that leaders will say in their own countries for domestic consumption."

But as for Karzai's latest remarks, "it was a head-scratcher," the official said.

The Wall Street Journal reported on Monday that Karzai had told lawmakers that the United States was interfering with Afghan affairs and that the Taliban would become a legitimate resistance movement if it did not stop.