A new report by the National Academy of Sciences committee, commissioned by the State Department. has discovered  that the U.S. embassy in Havana is most likely being targeted with waves of microwave radiation. This study found that the country has likely directed radiation at the embassy for the past four years.

Microwave radiation is a type of light invisible to the naked eye. When focused in highly concentrated amounts, this type of radiation becomes a weapon. Usually used to disable technology, the weapons cause brain damage in humans. The study examined and ruled out several other possible causes, including the use of insecticides in the area.

The findings come after years of a mysterious illness, dubbed the ‘Havana Syndrome,’ among American diplomats in Cuba. Symptoms include dizziness, loss of balance, loss of memory, anxiety, hearing loss, and difficulty thinking. Many diplomats impacted by the illness have sustained permanent brain damage. Several embassy employees were forced into early retirement as a result of severe symptoms.

The Canadian embassy has also been targeted by similar radiation. In early 2016, embassy employees complained of symptoms consistent with those experienced by their U.S. counterparts. The incident resulted in Canada quickly reducing its embassy personnel.

Scientists are unsure where the radiation impacting the embassies originated from. However, many intelligence officials suspect the Cuban government may be behind the attacks. If this is the case, the country likely gained access to the technology from either China or Russia.

This is not the first time U.S. citizens have been the target of longwave radiation. Over the past four years, diplomats working in China have described similar experiences. According to CBS News, fourteen cases of have been reported in China, though only one has been confirmed. Several C.I.A. officers have also encountered side effects eerily close to those in the Havana embassy. The separate instances occurred when traveling to overseas military bases to discuss counterintelligence against Russia.

The use of microwave radiation against Americans has become a bipartisan issue. Senators Susan Collins (R-ME) and Jeanne Shaheen (D-NH) have introduced a bill that would compensate C.I.A. and state workers that sustained brain damage “in connection with a war or hostile act.” This would include those impacted by microwave radiation.