A mysterious affliction called "Havana Syndrome" that has brought severe headaches, nausea and possible brain damage to US diplomats has many officials convinced they are under sustained attack using electronic weapons.
Last 24 August 2021, US Vice President Kamala Harris delayed for several hours a trip to Vietnam after the US embassy in Hanoi reported a possible case involving "acoustic incidents" there, raising concern she could be a target.
Ultimately Harris did go to Hanoi, and the State Department said it was investigating a case of what the US government officially dubs an "anomalous health incident" or AHI.
It was the most recent of dozens of such cases reported by US diplomats and intelligence officers since 2016, first in Cuba, then in China, Germany, Australia, Taiwan and in Washington itself.
In July, the New Yorker magazine reported there have been dozens of cases among US officials in Vienna, Austria since the beginning of 2021.
Amid concerns a powerful rival, possibly Russia, is mounting the attacks, the State Department has warned its thousands of diplomats of the threat while also carrying out extensive medical checks on those heading abroad so as to better measure any effects of future attacks.
"We take each report we receive extremely seriously and are working to ensure that affected employees get the care and support they need," a department spokesperson said.
The number of reported incidents among US officials has been kept under wraps.
After the Hanoi incident, former CIA operative Marc Polymeropoulos, himself a victim in Moscow in 2017, said the volume of attacks appeared to be mounting.