The reports published Wednesday by The Washington Post and the Associated Press say Mohammad Ibrahim Adel accepted the money, shortly after the Afghan government awarded the multi-billion dollar project to the state-run China Metallurgical Group in 2007.
The articles quote unnamed U.S. officials who are said to be familiar with reports of the incident.
Adel denies the allegations.
The Chinese firm is expected to invest nearly $3 billion, and pay the Afghan government royalties of some $400 million per year, to tap into one of the world's largest unexploited copper deposits.
