The United States sanctioned on Thursday five individuals and seven companies connected to Iran’s nuclear program.

Salim Borji, Mohammad Fakhrzadeh, Afsaneh Karimiadegani, Mehdi Najafi and Sohayl Talebi were sanctioned. The latter four are associated with the Iran Centrifuge Technology Company, which is already sanctioned by the United States, while Borji is connected to the Tamin Kalaye Sabz Aras Company, one of the seven entities designated.

The other entities sanctioned were Bakhtar Raad Sepahan Company; Henan Jiayuan Aluminium Industry Co., Ltd.; Sanming Sino-Euro Import And Export Co., Ltd.; Suzhou A-One Special Alloy Co., Ltd.; Suzhou Zhongsheng Magnetic Industry Co., Ltd.; and Tawu Mechanical Engineering and Trading Company.

Tamin Kalaye Sabz Aras, Sanming Sino-Euro Import and Export, Tawu Mechanical Engineering and Trading, Henan Jiayuan Aluminium and Bakhtar Raad Sepahan are connected to the Iran Centrifuge Technology Company, while Suzhou A-One Special Alloy and Suzhou Zhongsheng Magnetic are associated with Tamin Kalaye Sabz Aras.

“Treasury is taking action to shut down an Iranian nuclear procurement network that leverages Chinese- and Belgium-based front companies to acquire critical nuclear materials and benefit the regime’s malign ambitions. Iran cannot claim benign intent on the world stage while it purchases and stockpiles products for centrifuges,” said U.S. Treasury Secretary Steven Mnuchin. “The U.S. government is deeply concerned by the Iranian regime’s uranium enrichment and other provocative behaviors, and will continue to target all who provide support to Iran’s nuclear program.”

In a Catch-22, these sanctions come as the United States has offered Iran the opportunity for negotiations, which Tehran has refused unless U.S. sanctions against the regime are lifted.

Tensions between the two sides have sharpened since the Trump administration withdrew the United States from the Iran deal in May 2018, reimposing sanctions lifted under it, in addition to enacting new financial penalties against the Islamic Republic.