The concerns were sparked by Karzai’s decision this week to order a probe of two anti-corruption units that have been involved in the recent arrest of several senior government officials on graft and bribery allegations. Karzai said the investigators, who have been aided by U.S. law enforcement advisers and wiretap technology, were acting outside the Afghan constitution.

Afghanistan’s attorney general said on Thursday that Karzai plans to issue a decree outlining new regulations for the bodies, the Major Crimes Task Force and Special Investigative Unit.

Officials in Washington have moved urgently to ensure that anti-corruption efforts are not derailed. Secretary of State Hillary Rodham Clinton, the most senior U.S. official to discuss the matter with Karzai this week, conveyed the message that “these two anti-corruption bodies represent important progress,” a senior administration official said, “and any steps to undercut or remove powers or authorities from them would be a step backwards.”