Foreign Ministry spokesman Geng Shuang said China appreciated Iran's "strict implementation" of its 2015 nuclear deal, which U.S. President Donald Trump withdrew from a year ago.
"We regret that the U.S. has further aggravated the tension on the Iranian nuclear issue," Geng said.
"We call on all parties concerned to exercise restraint, strengthen dialogue and avoid escalating tensions," he said.
China's expression of support came despite a threat from Iran on Wednesday to resume higher enrichment of uranium in 60 days if world powers fail to negotiate new terms for the 2015 deal. President Hassan Rouhani said Iran will stop exporting its excess uranium and heavy water from its nuclear program, as stipulated by the agreement. If the 60-day deadline passes without action, Rouhani said Iran will resume higher uranium enrichment as well.
Geng's comments follow moves by Washington to deploy an aircraft carrier and a bomber wing to confront unspecified threats from Tehran. The U.S. withdrawal from the nuclear deal, formally known as the Joint Comprehensive Plan of Action, has already halted promised international business deals and dealt a heavy blow to Iran's already anemic economy. In the time since, the Trump administration has said any country that imports Iranian crude oil will face U.S. sanctions.
A key Iranian ally and trading partner, China was a signatory to the deal and continues to support it, along with Britain, Russia, China, the European Union, France and Germany.