Tensions between the U.S. and China may re-escalate after officials of both countries hurled verbal attacks at each other about the origin of the coronavirus, observers say.

In his Thursday tweets, Zhao Lijian, a spokesperson of China's Ministry of Foreign Affairs (MOFA), accused the U.S. of spreading the virus to the city of Wuhan in Hubei province, the epicenter of China's coronavirus outbreak.

The Chinese diplomat first posted a video clip in which Robert Redfield, director of the U.S. Centers for Disease Control and Prevention (CDC), told a congressional hearing Wednesday that some deaths from coronavirus have been discovered posthumously in the U.S.

Zhao then tweeted, "the U.S. CDC director was caught red-handed. When did patient zero emerge in the U.S.? How many people had he infected? What's the name of the hospital?"

An explanation

FILE - Chinese Foreign Ministry new spokesman Zhao Lijian gestures as he speaks during a daily briefing at the Ministry of Foreign Affairs office in Beijing, Feb. 24, 2020.

"It's possible that the U.S. military brought the virus to Wuhan. The U.S. has to be transparent and make public its figures. The U.S. owes us an explanation," he added.

Zhao's comments echoed a rumored conspiracy, widely circulated in China, that U.S. military personnel had brought the virus to China during their participation of the 2019 Military World Games in Wuhan last October.

That conspiracy theory followed suspicion raised by U.S. Senator Tom Cotton and others that the virus had originated from the Wuhan P4 lab, a high-security biochemical lab affiliated with the Chinese Academy of Sciences.

Cover-up

FILE - National security adviser Robert O'Brien addresses media during a news conference in Berlin, Jan. 20, 2020.

Zhao's comments also came one day after U.S. National Security Adviser Robert O'Brien asserted an initial cover-up of the virus in China "cost the world community two months" and exacerbated the global outbreak.

In response to O'Brien's claim, another MOFA spokesman, Geng Shuang, Thursday called it a "smear on the Chinese government and its people. It is immortal, irresponsible and of little help to the U.S.'s own fight against the outbreak."

No scientists have determined the source of the virus.

On Friday, the South China Morning Post newspaper cited China's government records saying the first person suffering from the disease can be traced to November 17, although "patient zero" in China has yet to be confirmed. The government records cited by the newspaper could help scientists track the spread of the disease and perhaps determine its source, it added.

Mixed reaction

Zhao's comments drew a whirlwind of mixed reaction on Twitter.

Some people, apparently from China, agreed with Zhao's assessment, while others called him a "shame."

"When will the U.S. stop escaping reality? This is outrageous," Lin Shaojing wrote in response to Zhao's tweet.

Many more, however, disagreed.

"A MOFA spokesman made such a conspiracy to confuse the public … Shame on you," Mr. Huang tweeted.

"Why not look into the Wuhan P4 Lab? It's possible that the lab leaked the virus to the downtown area. The lab needs to be transparent and make public its figures. The lab owes us an explanation," he added.

Another Twitter user named Cheryl also questioned, "if it were the U.S. which spread the virus, why did you help cover it up, shift the blame to the bat and reprimand whistleblower doctors? Do you also wish the Chinese dead?"

The verbal attacks between officials of both governments will do nothing but harm U.S.-China relations, which are already bad, said Jean-Pierre Cabestan, political science professor at Hong Kong Baptist University.

The professor said Zhao's accusation is groundless and doesn't make sense, although he said he doubted the U.S., caught up in its own fight against the virus, would respond.

Shifting blame

Zhao's narratives likely suggest China is trying to shift the blame, since public resentment toward the leadership's mishandling of the outbreak hasn't subsided, he said.

"So, one answer is to … certainly accusing the U.S. of being responsible of everything [so] as to call on the people to point to another threat and enemy for diversion of the people's resentment," Cabestan said.

Also, the Communist leadership is likely divided over how to ease public anger as state censors have recently eased their controls by having left some media reports critical of the government uncensored for a short period of time, according to the professor.

Those include a report about Ai Fen, director of Wuhan Central Hospital's emergency department, who called herself the one giving out whistles as she is actually the first to sound the alarm by sharing a diagnostic report with colleagues including the deceased whistleblower doctor Li Wenliang.

FILE - People attend a vigil for Chinese doctor Li Wenliang, in Hong Kong, Feb. 7, 2020. Li, who got in trouble with authorities for sounding an early warning about the coronavirus outbreak, died Feb. 7, 2020, after being infected.

In the report, Ai spoke out against local authorities to detail how she was reprimanded and forced to shut up. But she regretted that she hadn't been brave enough to speak up.

Meanwhile, Shi Yinhong, an international relations professor at Beijing's Renmin University, downplayed Zhao's accusation, saying the U.S. government shouldn't overreact to Zhao's personal comments.

"Up to date, the Chinese government hasn't made any statements or, in any official occasions, accused the U.S. military of having had brought the disease to China. The Chinese government has never said so," the professor said.

"We'd rather believe that this gentleman made the comments in his personal capacity and through his personal Twitter account. His views thus are of no significance," he added.

Shi urged the U.S. government and its politicians not to be overly concerned, saying both countries should focus their efforts on fighting the disease and bolstering their own economies.