"China's trade with Iran is normal business exchange, which will not harm the interests of other countries and the international community," Foreign Ministry spokeswoman Jiang Yu said in comments published Thursday in the China Daily newspaper.
"As a permanent member of the U.N. Security Council, China has always observed the council's resolutions," Jiang said.
The comments come after the U.S. State Department's special adviser for nonproliferation and arms control, Robert Einhorn, this week said China should fully support the newest U.N. sanctions on Iran.
The U.S. and others worry Iran's nuclear program could be used for weapons. Iran says its program is intended solely for peaceful purposes such as energy generation.
China often says dialogue and diplomatic means are the best way to resolve the Iran nuclear issue, and it has opposed the recent unilateral sanctions imposed on Iran both by the United States and the European Union.
The sanctions target Iran's foreign trade, banking and energy sectors.
China has vast energy needs and has large investments in Iran, and its position as a veto-wielding permanent member of the Security Council can challenge further U.N. pressure on the issue.