China said Wednesday it opposed "unilateral" sanctions against Iran, after US President Barack Obama signed into law new measures targeting the Islamic republic's central bank.

Washington's move came after the United States, Britain and Canada said in November they were slapping additional sanctions on Iran, citing evidence that Tehran is pursuing nuclear weapons.

Tehran denies the allegations, saying its nuclear programme is exclusively for medical and power generation purposes, and China has repeatedly said sanctions will not resolve the issue.

"China opposes placing one's domestic law above international law and imposing unilateral sanctions against other countries," said foreign ministry spokesman Hong Lei in response to a question about US sanctions on Iran.