A group of US diplomats and employees with 'Havana Syndrome' symptoms say the Biden administration is denying them care and ignoring their evidence

• US diplomats and staffers around the world have reported symptoms of the mysterious "Havana Syndrome."
• Twenty-one of them wrote a letter criticizing the Biden admin for not supporting them enough.
• They say they were not given enough medical support and had their evidence ignored.

A group of US diplomats and employees who say they've suffered from the so-called "Havana Syndrome" have written a letter criticizing the government's response to them, saying they have been denied proper medical care and had their evidence ignored.

The "Havana Syndrome" is a mysterious condition that has afflicted American staffers around the world, including in Cuba and China, that some experts have attributed to microwave attacks.

In the May 25 letter to the State Department obtained by NBC News, the officials listed a series of what they deemed failings in the US government response to the officials falling ill with the condition. The letter was sent on behalf of 21 officials US officials and their spouses diagnosed with actual or possible Havana syndrome, NBC News reported.

They said the State Department continues to "1) Deny employees and injured family members access to proper medical evaluation and treatment 2) Reject scientific evidence regarding the injuries and treatment needs and 3) Invalidate our injuries and experiences."

In contrast, they claim, military and intelligence officials with the syndrome "have had a different level and frequency of engagement."

"After four years of challenges, we were hopeful that the new administration would welcome a partnership with us to ensure those affected receive the care and treatment they need and ensure appropriate care for the new cases," the staffers wrote.

"Unfortunately, our experience thus far has fallen short of our renewed expectations."

Last October, CIA and State Department employees told The New York Times they were fighting for proper treatment, with one suggesting a cover-up by then-President Donald Trump's administration.

Insider has contacted the State Department for comment on the May 25 letter.

The department told NBC News that Secretary of State Antony Blinken was receiving regular updates about the situation and has "made clear that this is a priority for him." It added that the investigation into the cause of the syndrome was ongoing.

Reports of a mysterious syndrome suffered by US diplomats serving in Havana, Cuba, first began to emerge in 2016.

They reported concussion-like symptoms including headaches, dizziness and nausea, which in some cases have required months of medical treatment. Some reported hearing a loud piercing noise just before the onset of symptoms.

CNN reported that some officials have been diagnosed with traumatic brain injuries, and continue to suffer from symptoms including headaches years after the attack.

There has been a sharp uptick in cases in recent months, with a New York Times report earlier this month citing a total of 130 cases recorded so far.

Two recent cases have occurred in Washington DC, one in the environs of the White House, increasing pressure on the Biden administration to establish what is causing the officials to fall sick.

Politico reported that US intelligence believes that the GRU, the Russian military intelligence agency, may be behind the attacks.

Federal government agencies are attempting to establish the cause of the syndrome. A report by the National Academies of Science last December found that the syndrome was likely being caused by directed microwave radiation. While not attributing any blame for the incidents, the scientists noted that research into microwave attacks had been conducted by the Soviet Union.

A bipartisan group of US senators last week unveiled legislation to provide greater financial support for those with brain injuries caused by the syndrome.