Austria and the US said  they were investigating reports of US diplomats and other officials in Vienna falling sick with health problems similar to the so-called “Havana syndrome”.

US senators in May said that the government was investigating an apparent increase in mysterious directed-energy attacks, amid new reports of potentially brain-damaging incidents inside the US.

The still unexplained attacks have caused sickness and even brain damage in US diplomats and intelligence officials in Cuba, China, Russia and other countries.

Moscow is suspected to be behind them, even if the mechanism for them has yet to be explained. Scientists have theorised that the attacks arise from pulsed microwaves.

Since the first attacks were reported in Cuba in 2016, and after that in China, scientists and doctors have debated the causes and effects, without a uniform conclusion.

The New Yorker reported on Friday that since Joe Biden took office this year, about two dozen US intelligence officers, diplomats and other government officials in Vienna have reported problems similar to the “Havana syndrome”.

Austria’s Foreign Ministry said in a statement that it was “working with the US authorities on a joint investigation in accordance with our role as the host state”.

“We take these reports very seriously…. The safety of the diplomats sent to Austria and their families is our top priority,” it said without giving further details.

A US State Department spokesperson said they were “vigorously investigating reports of possible unexplained health incidents (UHI) among the US Embassy Vienna community or wherever they are reported”.

The official added that “any employees who reported a possible UHI received immediate and appropriate attention and care”.

Among other steps, the US has already set up a team of medical experts that can address these problems globally and is working to “better protect against these events in the future”, the official added.

Austria hosts a large corps of foreign diplomats working at several Vienna-based UN and other international organisations