US still seeking clues to mystery illness afflicting diplomats and spies

Starting in late 2016, dozens of US officials and family members living in Cuba and China or travelling for work in other countries, including Russia, reported contracting an illness that has become known as Havana Syndrome, based on where it first publicly emerged.

The symptoms included headaches, memory loss, vertigo, nausea, bloody noses and hearing strange sounds.

Some US officials, including experienced CIA analysts, and scientists believe the victims were targeted by a foreign adversary wielding weaponised microwave radiation. Russia beamed microwaves at the US Embassy in Moscow in the 1970s and 1980s, and it has more recently harassed diplomats and fuelled violence against US soldiers.

Other US officials and scientists say the injuries may be the product of a psychological illness, or even pesticides.

Mr Pompeo, who was the CIA director before leading the State Department, said the government was still examining multiple theories in what he described as "a very complicated situation".

There is not yet any complete US government analysis which definitively tells us precisely how these all came to be, whether they're part of a single cohort," Mr Pompeo said at a news conference.

"There are significant US government resources now, what, three-plus years on, devoted to getting to the bottom of this and then holding those responsible accountable - should we determine that that's required," he said.

Mr Pompeo was responding to a reporter's question about what the State Department was doing to protect diplomats, and why there appeared to be deep disparities in the response to the episode in Cuba compared to the one in China. Mr Pompeo took umbrage at the question.