China has found no clues to determine what caused a US government employee to suffer a brain trauma after experiencing unusual sounds, the foreign ministry said Thursday.

The US State Department has said the incident in the southern city of Guangzhou resembled the still-unexplained injuries that befell US and Canadian diplomats in Cuba last year.

The US Consulate General in Guangzhou. Photo: US Gov.

“China has conducted a very careful investigation and has given preliminary findings to the US, and we haven’t found the reason or clues that led to the situation mentioned by the US,” foreign ministry spokesman Lu Kang told a regular press briefing.

“China has always followed the Vienna Convention on diplomatic relations and consular relations to protect the US diplomatic staff and staff from other countries,” Lu said.

The US embassy in Beijing issued a health alert Wednesday over the incident, while saying it did not know what caused the symptoms or of any similar situations in the country.

The health alert said the employee “recently reported subtle and vague, but abnormal, sensations of sound and pressure”.

The unidentified US citizen experienced a variety of physical symptoms between late 2017 and April 2018. The person was sent to the United States for further evaluation and on May 18 the embassy learned that the victim had mild traumatic brain injury (MTBI).

During a visit to Washington on Wednesday, Chinese Foreign Minister Wang Yi said China had not “found that any organisation or individual has carried out such a sonic influence”.

Wang warned against the case being “politicised”.

US Secretary of State Mike Pompeo said the medical indications were “very similar and entirely consistent” with what happened in Cuba.

“We are working to figure out what took place both in Havana and now in China as well,” he said.

Last year 24 US diplomats and their family members in Cuba fell victim to mysterious “attacks” that left them with injuries resembling brain trauma. Ten Canadian diplomats and their relatives also suffered a strange illness.

Both countries scaled back their presence on the Caribbean island due to the problem, which continues to baffle investigators and has strained US diplomatic relations with Havana.

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