A prominent campaigner against Vladimir Putin fears she was poisoned by a “some kind of nerve agent” while at Russian opposition meetings in Berlin or Prague.
The FBI is now investigating Natalia Arno's claims as she has lived in the US since she was exiled from Russia almost a decade ago.
Ms Arno, head of the Free Russia Foundation, claims she felt numbness and “severe pain” in her body after her hotel door was mysteriously left open and she detected what appears to be the “smell of cheap perfume”.
An unnamed woman journalist who recently fled Russia is also feared to have been poisoned, it has been claimed.
John Herbst, 70, a former US ambassador to Ukraine, now senior director of the Atlantic Council’s Eurasia Centre and a Putin critic, says he also experienced poisoning symptoms before the war started in Ukraine.
The case of Ms Arno, 47, is being investigated by the FBI, after she complained of strange symptoms when returning to the US, where she has lived since being exiled from her homeland in 2014, reported Agentstvo.
“The FBI launched an investigation, interviewed Arno, and took biological and physical samples, including clothing and other items [she] had with her while travelling, for examination,” said a report.
An unnamed Russian woman journalist also complained of symptoms in Berlin where both women attended a meeting of opposition activists organised by prominent Putin foe Mikhail Khodorkovsky, 59, once Russia’s wealthiest man.
The journalist evidently attended a clinic in Berlin which treated Alexei Navalny, 46, another opposition leader, now a political prisoner in Russia.
He had been poisoned by nerve agent Novichok in an assassination bid.
Kremlin critic Vladimir Kara-Murza, 41, who holds Russian and British citizenship, imprisoned for 25 years for criticising Putin’s war and opposing his regime, was twice poisoned.
Ms Arno - a professor in Russia before she was forced to leave - said: “There is a suspicion that during my recent trip to Europe [in late April and early May], I was poisoned, possibly by some kind of nerve agent.”
“One - or even more than one - Western intelligence agency is investigating.
“I still have neuropathy symptoms, but in general, I feel much better.”
She warned Russians who flee abroad from Putin’s regime and oppose his war seeking a free and democratic country "need to understand that the enemy has long tentacles.
“It is possible to endanger us outside Russia, so we need to always be vigilant, but not be afraid and not give up, be wiser, more coordinated and more resilient.”
She said: "After a busy day of discussions and meetings, I returned to my hotel in the evening and saw that the door to my room was slightly open.
“The first thought was: is Comrade Major [Russian secret services] really waiting inside?
“But then I thought it was paranoia, and either the maid accidentally left the door open, or Comrade Major's colleagues left the bugs [listening devices].
“I checked my things and the room, I didn’t find any bugs, but I immediately felt an extraneous and pungent smell of cheap perfume in the room.
“I needed to go further to the last meeting, so I left the hotel again, going to the reception and complaining about the open door.
“At the reception, they said that it was ‘the maid who forgot and she will definitely be scolded’.”
She added that when she came back the room appeared normal, but at 5am woke “with severe pain and strange symptoms”.
On her flight home to US her symptoms worsened - but when initial tests were carried out, nothing was detected.
