Afghan President Hamid Karzai's brother denies accusations that he is involved in Afghanistan's heroin trade and said his accusers can "hang me in Kandahar City" if they find proof showing otherwise.

Ahmed Wali Karzai was responding to claims by two unnamed U.S. officials, quoted in The New York Times, that the White House believes he has been involved in the bustling Afghan drug trade for the last five to six years.

They also accused him of releasing a truckload of drugs that had been seized by police.

"I am ready to swear in God's name, on my children's name that I never in my life, I never had anything to do with any kind of drugs in my life, not in the past, not now, and I will not do anything in the future," Karzai said Monday during a press conference. "If anybody can come and they can prove it, then they can hang me in Kandahar City."

Karzai, who is chairman of the Kandahar provincial council, said he is being targeted by American officials who are trying to undermine his brother's authority in Afghanistan.

"All these accusations are politically motivated, and I am the victim of vicious politics," Wali Karzai said. "Whenever the president of Afghanistan takes a stand against the international communities, it's always followed by articles against me. So I am a sort of punching bag for the president."

Wali Karzai said U.S. officials are upset that his brother ordered a review of U.S. and NATO military policies in Afghanistan.

Karzai made the announcement after an Aug. 22 American special forces operation in Herat province killed 90 civilians, according to Afghan officials.

A U.S. report said American and Afghan forces returned fire after being shot at by a group of militants. However, video evidence seemed to show that many of the dead were young children.

Afghanistan produces more than 90 per cent of the world's opium, which is used to make heroin. The opium industry rakes in billions of dollars, and U.S. officials believe much of that money is used to fuel the country's insurgency.

Most of the opium is produced in the southern part of Afghanistan, the most violent region of the country.

Wali Karzai invited his accusers to prove their allegations in court.

"How can they prove I'm guilty?" he said. "That's the question. It's my word against their word."

With files from The Associated Press