Sihai Cheng supplied thousands of parts that have nuclear applications to Eyvaz, a company involved in Iran’s nuclear weapons program, in violation of U.S. sanctions onIran, federal prosecutors said.

The indictment, unsealed on Friday, comes as Iran and six world powers are trying to negotiate a comprehensive agreement to address Western suspicions that Iran is seeking to acquire nuclear weapons.

The aim of the talks is to hammer out a long-term deal by July 20 that would define the permissible scope of Iran’s nuclear program in return for a lifting of sanctions that are severely battering its oil-dependent economy.

Cheng was arrested in the United Kingdom in February on a U.S. provisional arrest warrant, according to the U.S. Attorney’s office in Massachusetts, which is prosecuting the case.

He faces a hearing in June over whether he will be extradited to the United States.

Cheng could not be immediately reached for comment.