Beijing reacted furiously on Wednesday to new US sanctions imposed on a Chinese bank over transactions with Iran, urging Washington to revoke them and saying it would lodge an official protest.
China's foreign ministry urged the United States to lift the sanctions on the Bank of Kunlun and stop "damaging China's interests and Sino-US relations".
US President Barack Obama on Tuesday imposed new economic sanctions on Iran's oil export sector and on a pair of Chinese and Iraqi banks accused of doing business with Tehran.
Obama said the new measures underlined the United States' determination to force Tehran "to meet its international obligations" in nuclear negotiations, according to a statement released by the White House.
The US president accused the Bank of Kunlun and the Elaf Islamic Bank in Iraq of arranging transactions worth millions of dollars with Iranian banks already under sanctions because of alleged links to Tehran's weapons program.
In a brief statement, China's foreign ministry expressed "strong dissatisfaction and firm opposition" to the US move and said it would officially protest the decision.
"China has regular relations with Iran in the energy and trade fields, which have no connection with Iran's nuclear plans," the statement said.
The banking dispute comes after Washington and and Beijing clashed last month over proposed United Nations' sanctions against Syria, which were vetoed by China and Russia, provoking criticism by the Obama administration.