KABUL, Afghanistan – Afghanistan’s president vowed Friday to let Western-backed anti-corruption teams pursue inquiries free from political interference following two rounds of candid talks with U.S. Sen. John Kerry that Kerry said were marked by “sometimes tough” conversation.

Kerry, D-Mass., urged President Hamid Karzai to move quickly to combat corruption or risk losing support in the U.S. Congress at a critical phase in the war. U.S. lawmakers have expressed doubt the military effort can succeed without a serious campaign against the bribery and graft that have eroded the Afghan people’s trust in the Karzai government.

Kerry, who heads the Senate Foreign Relations Committee, met twice with Karzai on Tuesday and then returned for a second, unscheduled round of talks Friday after traveling to Pakistan to see areas devastated by massive floods. After the meeting, Karzai made his first public remarks about two investigative units instrumental in the recent arrest of one of Karzai’s top advisers.

Mohammad Zia Salehi, who has since been released pending charges, was arrested for allegedly accepting a car in exchange for his help in exerting pressure on Afghan officials to ease off in another corruption case.

U.S. officials view Salehi’s arrest as a test case of Karzai’s willingness to fight corruption.

Soon after Salehi’s arrest, Karzai met with members of a panel he set up to review the work of the Major Crimes Task Force and the Sensitive Investigative Unit, which conduct corruption probes of high-level Afghan government officials and then feed cases to Afghan prosecutors.

Earlier this month, Karzai released a statement saying all cases under investigation or completed should be reviewed by the panel and reported to the president.

That sparked concern that Karzai was attempting to derail corruption probes of top officials in his government.

Heightened pressure on Karzai to clean up corruption within the ranks of his government comes as the last of 30,000 U.S. reinforcements arrive, death tolls are rising and American public support for the war is eroding.