Foreign ministry spokesman Geng Shuang said the U.S. is operating outside its jurisdiction in unilaterally imposing the sanctions. He said normal interactions between Iran and other countries are "reasonable and lawful" and deserving of respect and protection.
"The relevant actions of the U.S. will also intensify the turmoil in the Middle East and international energy market," Geng said.
"We urge the U.S. to play a constructive role in a responsible manner, instead of the other way around. In addition, we have already made complaints with the U.S. on this matter," he said.
Geng said China will work to safeguard its companies' interests, reflecting its desire to secure foreign markets as it pursues its massive "Belt-and-Road" infrastructure initiative.
China is one of Iran's biggest oil markets and was a strong backer of the agreement to lift sanctions in return for Iran curbing its nuclear weapons program that was scrapped by President Donald Trump.
The Trump administration said Monday that it will no longer exempt any countries from U.S. sanctions if they continue to buy Iranian oil, stepping up pressure on Iran in a move that primarily affects the five remaining major importers.
Along with India and U.S. treaty allies Japan, South Korea and Turkey, China was one of the countries primarily affected by the announcement.
Oil prices soared to their highest level since October on Tuesday.
The sanctions could potentially remove up to 1.2 million barrels of oil per day from international markets, according to industry experts. However, that number will likely be lower, depending on how countries respond and just how much oil Iran continues to export.
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