The investigation, which Berlin’s city authorities confirmed to Der Spiegel last week, comes after at least two members of staff at the embassy reported symptoms that correspond to the so-called Havana syndrome, an unexplained sickness that has been affecting US diplomats and spies across the globe since 2016.

The US embassy has reportedly handed over evidence to Berlin’s state detective agency.

The first cases were reported in Havana, the Cuban capital, where dozens of diplomats reported suffering nausea and headaches. There have since been cases reported in Vienna, Moscow and Singapore.

US authorities suspect that the condition is caused by a sophisticated attack using concentrated microwaves.

The fact that many of the diplomats and CIA agents affected were working on Russian affairs has led them to believe that Moscow is somehow involved – a charge that the Kremlin denies.

As far as this so-called ‘syndrome’ is concerned, US President Joe Biden has vowed to find out “the cause and who is responsible.”