President Joe Biden on Friday signed a law providing financial support for victims of mysterious headaches and nausea suffered by US diplomats in what has been dubbed the "Havana Syndrome."

The Havana Act provides financial compensation for members of the State Department and CIA who suffer brain injury from what US officials suspect may be directed microwave attacks.

Dozens of cases have occurred at US embassies around the world, starting with a cluster in Havana, Cuba. The cause of the illnesses has not been fully diagnosed and the identity of the attacker, if there is one, has not been revealed.

"I want to thank Congress for passing it with unanimous bipartisan support, sending the clear message that we take care of our own," Biden said in a statement.

"Civil servants, intelligence officers, diplomats, and military personnel all around the world have been affected by anomalous health incidents. Some are struggling with debilitating brain injuries that have curtailed their careers of service to our nation."

Republican Senator Susan Collins, lead author of the law, said in a statement that "Havana Syndrome" illnesses have struck more than 40 US staff in Cuba, starting in 2016 and dozens more elsewhere, including some reportedly on US soil.

A member of CIA Director William Burns' team had similar symptoms in India this month, during a trip there by the intelligence chief, according to US media reports.

Two US officials in Germany were also among the recent victims and the New Yorker reported that there have been dozens of cases afflicting US officials in Vienna, Austria, alone.

Collins said the new law would give those suffering assistance.

"Far too many 'Havana Syndrome' victims have had to battle the bureaucracy to receive care for their debilitating injuries," she said.

"For those victims, the Havana Act will ensure that they receive the financial and medical support that they deserve. It also affirms our commitment to making sure that our government finds out who is responsible."