US officials believe the military intelligence unit could be responsible for the attacks on US government personnel around the world, according to Politico.
The officials say they do not have definitive proof of Russian involvement and the intelligence community has not made a final determination.
But lawmakers have now been told that federal officials have stepped up their investigation to include all 18 intelligence services and is focussed on the GRU, a congressional official briefed on the matter said.
“The health and well-being of American public servants is a paramount priority to the Administration and we take extremely seriously reports by our personnel of anomalous health incidents,” a White House spokesperson said.
The government has received reports of attacks with symptoms consistent with the 2016 “Havana syndrome”, which saw diplomats and spies struck down with headaches, loss of balance and hearing, pressure and ringing in the ears and in some cases brain damage.
The Russian military agency is known for its international operations, and is blamed by the British for the 2018 nerve agent attacks in Salisbury, when a former GRU officer living in the UK was poisoned.
The agency’s operatives have also been blamed for cyber hacking attacks, and for playing a role in Syria and Ukraine.
The incidents have allegedly occurred all over the world, including in Europe, as well as Miami, northern Virginia and near the White House, according to Politico.
“It looks, smells and feels like the GRU,” said one former national security official who is involved in the probe.
“When you are looking at the landscape, there are very few people who are willing, capable and have the technology. It’s pretty simple forensics.”
Another officials told Politico that GRU agents “are the only ones [we] know have the capability to attack our people like that on our soil”.
Experts say that China and Israel also have the technology needed for the attacks, but that they do not operate in every location where they were carried out.