BEIJING (Reuters) - China has found no clues to explain what happened to an American citizen working at a U.S. consulate who reported suffering from “abnormal” sounds and pressure leading to a mild brain injury, a foreign ministry spokesman said on Thursday.

FILE PHOTO: Chinese Foreign Ministry spokesman Lu Kang answers questions about a major bus accident in North Korea, during a news conference in Beijing, China April 23, 2018. REUTERS/Jason Lee/File Photo

The U.S. embassy, which issued a health alert on Wednesday to Americans living in China, said it could not link the case to health problems suffered by U.S. government staff in Cuba dating back to late 2016.

Foreign Ministry spokesman Lu Kang said China has always safeguarded the security of foreign organizations and personnel of foreign countries, including the United States, according to the Vienna convention.

“China has already conducted an earnest investigation and we have also given initial feedback to the U.S. side,” Lu told a daily news briefing in Beijing.

“Currently, we have not found any reasons or clues leading to the situation described by the United States,” he said.

In Washington on Wednesday, U.S. Secretary of State Mike Pompeo said the United States was concerned about the “serious medical incident” and raised it with China’s visiting State Councillor Wang Yi.

The unnamed U.S. citizen assigned to the consulate in the southern city of Guangzhou had reported various “physical symptoms” dating from late 2017 to April this year, the U.S. embassy in Beijing said in an email.

The worker was sent to the United States for further evaluation. “The clinical findings of this evaluation matched mild traumatic brain injury (MTBI),” the embassy said.

The State Department will send a medical team to Guangzhou early next week to conduct baseline medical evaluations of all consulate employees who request it, State Department spokeswoman Heather Nauert said.

China’s nationalistic state-run Global Times tabloid said in a commentary late on Wednesday that it was “very inappropriate” that the United States issued a public health alert despite only having a “vague understanding” of the situation.

It said it was “inconceivable” that China would carry out targeted attacks on the health of foreign diplomats.

“We firmly believe that there is not much possibility of any ‘background’ to the American consulate official’s ‘brain injury’,” it said.

The U.S. government in October expelled 15 Cuban diplomats from the United States for what it said was Cuba’s failure to protect staff at the U.S. embassy in Havana from mysterious health incidents at one point thought to possibly have been acoustic “attacks”.

Staff there reported symptoms including hearing loss, dizziness, fatigue and cognitive issues, though Cuban officials dismissed the idea of acoustic strikes as “science fiction” and accused Washington of slander.

The cause of those incidents remains unresolved.

The Canadian government in April said it would remove families of diplomats posted to Cuba after Canadian personnel there in 2017 also reported similar health symptoms.