China’s ambassador to the U.S. reaffirmed his opposition to promoting theories that the virus that causes Covid-19 originated in an American military lab, in an unusual break with the country’s foreign ministry.

Chinese Ambassador Cui Tiankai said in an interview with “Axios on HBO” that he stood by his Feb. 9 statement that it would be “crazy” to spread such theories. Since his original remarks, the Ministry of Foreign Affairs in Beijing has repeatedly posted statements speculating about a possible U.S. origin for the virus, which was first detected in the central Chinese city of Wuhan.

“Such speculation will help nobody. It’s very harmful,” Cui said in the interview that aired Sunday. “Eventually, we must have an answer to where the virus originally came from. But, this is the job for the scientists to do, not for diplomats.”

Cui’s comments represent a sharp public rebuke to Foreign Ministry spokesman Zhao Lijian, who has publicly questioned whether the virus originated in China and even touted the idea that it may have been introduced by U.S. Army athletes. Such public differences are rare among Chinese officials who are famous for their ability to stick closely to the Communist Party’s official line.

Cui is appointed directly by President Xi Jinping and holds a vice-ministerial rank in China’s political hierarchy. That makes him two levels senior to Zhao, whose official title is deputy director of the foreign ministry’s Information Department.

Zhao continued to promote the theory Sunday, retweeting speculation from a Twitter user who goes by the name “the lizard king” that COVID-19 has been around in America “for a while.” The user is described as a “fl transplant to the desert,” a “mama” and “not an expert.”

The ministry spokesman’s statements have been echoed in official state media in recent days and have provoked anger in Washington. President Donald Trump has taken to calling the pathogen the “Chinese virus” and has blamed the U.S.’s outbreak on the Asian country’s early failures to control the disease.

“As you know China tried to say at one point -- maybe they stopped now -- that it was caused by American soldiers,” Trump told reporters March 18. “That can’t happen. It’s not going to happen, not as long as I’m president. It comes from China.”

China Guts U.S. Press Corps in Beijing With Mass Expulsions

Meanwhile, China has also found itself in a tit-for-tat with the Trump administration over foreign journalists in Beijing. Last week, authorities in the foreign ministry expelled at least 13 American journalists from Beijing and forced at least seven Chinese nationals to stop working for American news outlets there.

Asked by Axios about Zhao’s comments, Cui referred the question back to the spokesman and his authority as ambassador to speak on behalf of the Chinese government.

“Maybe you could go and ask him,” Cui said. “I’m here representing my head of the state and my government.”

— With assistance by Peter Martin