Secretary of State Mike Pompeo told a Congressional panel Wednesday that a “sonic attack” on a U.S. official reported in Guangzhou, China, was similar to incidents in Cuba where U.S. diplomats later became ill.

“The medical indications are very similar, and entirely consistent with, the medical indications that were taking place to Americans working in Cuba,” Pompeo said during testimony to the House Foreign Affairs Committee about the possible U.S.-North Korea summit.

He said that medical teams are en route to the southern Chinese city to investigate the mysterious incident.

The State Department issued a health alert earlier Wednesday after a government employee stationed in Guangzhou was diagnosed with a mild traumatic brain injury. The official reported “subtle and vague, but abnormal, sensations of sound and pressure,” the State Department reported.

The alert cautioned any personnel in China who experienced “acute auditory or sensory phenomena accompanied by unusual sounds or piercing noises” to leave the area.

The report of the mysterious incident comes at a sensitive time for U.S.-China relations. The Trump administration recently threatened to impose steep tariffs on Chinese imported goods unless Beijing pledges to make big cuts in its trade surplus with the U.S. China, in turn, retaliated with threats of big tariffs on farm products and auto parts.

Trump said Tuesday that his administration also may seek a fine of as much as $1.3 billion against Chinese telecom company ZTE and demand management changes. The administration barred U.S. companies from selling components to ZTE, saying the company had violated American sanctions on North Korea and Iran. The Chinese firm has said the ban threatened its survival.

The health warning from the State Department Wednesday recalled a series of so-called “sonic attacks” on American diplomats in Cuba. Those incidents, still unexplained, prompted the withdrawal of most U.S. embassy personnel from the capital city of Havana in 2016. The recall followed multiple complaints of symptoms including hearing loss, dizziness, visual impairment, headaches and fatigue.

In January, then-Secretary of State Rex Tillerson told the Associated Press he wasn’t convinced that what he called “deliberate attacks” in Cuba were over. He defended his decision to withdraw most U.S. embassy staff.

“I’d be intentionally putting them back in harm’s way. Why in the world would I do that when I have no means whatsoever to protect them?” Tillerson told the AP in January.

“I still believe that the Cuban government, someone within the Cuban government can bring this to an end,” Tillerson added.

The Trump administration has never claimed Cuba perpetrated the attacks, but it has insisted Havana must know who did. Cuba has denied both involvement and knowledge of any attacks.

In an interim FBI report, the bureau said it found no evidence that sound waves could have damaged the Americans’ health, according to the AP.

The bureau tested a hypothesis that air pressure waves carried by audible sound could be used to clandestinely hurt Americans in Cuba, but found no evidence. The FBI report didn’t address other theories, and said it would continue investigating until it could demonstrate there had been no intentional harm, according to the report

The cause of the injuries reported in Cuba remains a mystery.

The Associated Press contributed to this report.