China has vowed to protect its interests after the US announced plans to widen economic sanctions against Iran and its trading partners, which include Beijing.

Foreign ministry spokesman Lin Jian said China was firmly opposed to what it called “illegal unilateral sanctions” and would take “all necessary measures” to safeguard its rights.

This came after US Treasury Secretary Scott Bessent announced the new measures on Monday, warning any nation financially partnering with Iran would be isolated.

China is the biggest buyer of Iranian oil, although the trade has declined under the US blockade of the Strait of Hormuz.

Lin said: “Cooperation between China and Iran has always been conducted within the framework of international law and should not be interfered with or disrupted.”

Bessent described the new measures as “the single greatest financial offensive ever” against Iran, warning banks and businesses would share in Iran’s isolation if they refused to cut ties with the country.

He declined to focus on specific nations, but said US President Donald Trump would be phoning world leaders “with specific requests to cease their interactions with the regime”.

However, responding to a question about Chinese banks, Bessent said he wanted to make clear “no one was above the reach of US sanctions”.

The announcement comes ahead of planned talks between Trump and Chinese President Xi Jinping next month.

Washington is likely to be wary of potential retaliation from Beijing, which processes the majority of the world’s rare earths and other critical minerals, crucial in the manufacture of many high-tech products.

Beijing has already tightened export controls on rare earths as part of previous trade negotiations with the US.

China’s response followed Iranian Economy Minister Ali Madanizadeh saying Tehran was “fully prepared” for the wider sanctions, which he said would lead to “another defeat” for the US.

“The government is and was ready and has a two-year plan to manage these events,” he told state television, adding Tehran had been “waiting for these plans for a long time”.

“We also have our own tools and know how to play the game,” he said.