The United States on Thursday said it blacklisted two companies based in Hong Kong, one in Shanghai and one in Dubai for helping Iran’s state-owned National Iranian Oil Company (NIOC) export millions of dollars of goods in violation of U.S. sanctions, Reuters has reported.

The U.S. Treasury Department said it imposed sanctions on the Hong Kong-based Triliance Petrochemical Co. Ltd and Sage Energy HK Limited, China-based Peakview Industry Co Ltd and United Arab Emirates-based Beneathco DMCC.

The sanctions would freeze all assets held by the companies that fall under U.S. jurisdiction, generally bar U.S. companies and individuals from dealing with them, and potentially subject non-U.S. financial institutions that knowingly facilitate “significant transactions” for them to U.S. sanctions.

In addition, the U.S. government-imposed sanctions on two other companies, Jiaxiang Industry Hong Kong Limited and Shandong Oiwangwa Petrochemical Co Ltd, and two individuals, Ali Bayandrian, who is linked to Triliance Petroleum, and Zhiqing Wang, a Chinese national linked to Shandong Oiwangwa.

U.S.-Iranian tensions have risen since the U.S. decision to abandon the 2015 Iran nuclear deal, its subsequent re-imposition of U.S. sanctions on the Islamic Republic, attacks on Saudi oil facilities blamed on Iran and the U.S. drone strike that killed Iranian military commander Qassem Soleimani in early January.