President Joe Biden’s administration said that it still remained committed to diplomacy with Iran to restore a 2015 agreement on curbing its nuclear program.

“Absent a deal, we will continue to use our sanctions authorities to limit exports of petroleum, petroleum products and petrochemical products from Iran,” said Brian Nelson, senior Treasury Department official.

The Treasury Department said it was imposing sanctions on a network of Iranian petrochemical firms including alleged front companies in China and the United Arab Emirates for Iran’s state-owned company and Triliance, a Hong Kong-based company already under US sanctions for its dealing with Iran.

It also took action against China-based broker Jeff Gao and Indian national Mohammad Shaheed Ruknooddin Bhore for allegedly managing business for Triliance.

The United States has sought to prevent any nation from buying Iranian oil since 2018 after then president Donald Trump walked away from a negotiated agreement, in which Iran drastically scaled back its nuclear program in return for promises of sanctions relief.

China has remained the top buyer of Iranian oil while India reluctantly ended imports under US pressure.

Biden has sought to restore the nuclear deal, saying that the United States would ease sanctions if Iran returns to compliance, but his chief negotiator recently said it was more likely than not that the diplomacy will fail.

Iran has insisted on the United States removing a Trump-era designation of its powerful Revolutionary Guards as a terrorist organization, a move that Biden has rejected as peripheral to discussions on the nuclear deal.