The Biden Administration will pressure China to stop importing Iranian crude oil, US Special Envoy for Iran Robert Malley told Bloomberg television on Tuesday.

“China is the main destination of illicit exports by Iran” and the United States will intensify talks to dissuade Beijing not to break US sanctions, Malley told Bloomberg.

The Trump administration imposed third-party sanctions on Iran’s oil exports after it withdrew from the 2015 nuclear accord, but China increased its purchases when President Joe Biden got elected and pledged to return to the agreement known as the JCPOA.

Latest estimates are that small Chinese refineries are buying at least 700,000 barrels per day at discounted prices through middlemen and illicit channels. Beijing does not officially report the Iranian oil cargoes as they are usually labeled as shipments from other countries.

Some reports say Iranian oil shipments increased in December, but it is not clear if exports to China have surged or more exports are sent elsewhere, such as Venezuela.

Critics have been accusing the Biden administration of not exerting enough pressure on Beijing to stop imports from Iran, hoping that China will play a positive role in nuclear talks with Tehran. These negotiations came to a halt last September and since then the US and its European allies have adopted tougher positions against Iran, for its human rights violations and supplies of kamikaze drones to Russia.