The US embassy’s latest health alert, the second in two weeks, for China over a mysterious illness has revived fears of a rumoured sonic weapon that first surfaced after a scare involving American diplomats and their families in Cuba two years ago.
Doctors examined the staff, who fell ill after hearing strange sounds at a consulate in the southern Chinese city of Guangzhou, with several workforces evacuated to the US and at least one diagnosed with brain trauma.
The new cases eerily echo the odd noises and subsequent illnesses suffered by 24 US diplomats evacuated from Cuba since 2016, deepening a baffling medical enigma. But the incident also poses a diplomatic conundrum - how to respond to what some fear may be a deliberate attack against Americans by shadowy foes on Chinese soil.
According to a New York Times report, US officials have privately raised questions about whether China or Russia, might have separately or in tandem targeted the diplomats. Washington has so far taken care not to implicate Beijing, which has told US officials it is investigating the incident.
"Until they are certain of the cause, it seems premature to make accusations," said Bonnie Glaser, a China expert at the Centre for Strategic and International Studies in Washington. "I don't think the US is calling it an 'attack'."
It is in stark contrast to the US handling of the Cuba case when the State Department lashed out at Havana for failing to protect its diplomats.
As a rising superpower, Beijing possesses significantly greater clout than impoverished Havana, with the cases coming at a precarious moment in US-China relations.
Ongoing talks to avoid a full-blown trade war are balanced on a knife-edge, and Beijing's cooperation is likely to be key if hopes for North Korea's denuclearisation ahead of next week's summit between Trump and Kim Jong Un are to be realised.
Still lacking proof to support allegations against Cuba, US officials could also be facing up to claims there were no "sonic attacks" after all.
Although the American victims heard strange noises -- described as static or the sound of metal sheets waving -- studies have cast doubt on the "acoustic weapon" hypothesis.
(With inputs from agencies)