The inquiry is being handled by the state security unit, a specialised team that examines cases related to ‘terrorism’.

German police say they are investigating the possible poisoning of two Russian exiles who last month attended a conference in Berlin organised by a Russian Kremlin critic, Mikhail Khodorkovsky.

Berlin police told the Reuters news agency on Sunday that “a file had been opened” after German newspaper Welt am Sonntag, citing Russian investigative media group Agentstvo, said two women reported symptoms that suggested possible poisoning.

The investigation is being handled by the state security unit, a specialised team that examines cases related to “terrorism” or politically motivated crimes, a Berlin police spokesman told the AFP news agency.

“An investigation has been opened. The probe is ongoing,” he said, declining to provide further details.

Russian investigative media outlet Agentstvo last week published a report saying two participants who attended an April 29-30 meeting of Russian dissidents in Berlin experienced health problems.

One participant, identified as a journalist who had recently left Russia, experienced unspecified symptoms during the event. They said the symptoms may have started earlier.

The report added that the journalist went to the Charite University Hospital in Berlin – where Kremlin critic Alexey Navalny was treated after being poisoned in August 2020.

The second participant mentioned was Natalia Arno, director of the NGO Free Russia Foundation in the United States, where she has lived for 10 years since having had to leave Russia.

Arno had attended the Berlin meeting of dissidents before travelling to Prague, where she experienced symptoms and discovered that her hotel room had been opened, Agentstvo reported.

Leaving the next day for the US, she contacted a hospital there as well as the authorities.

Arno detailed her problems – “sharp pain” and “numbness” – on Facebook this week, saying the first “strange symptoms” appeared before she arrived in Prague. She said she still had symptoms but felt better.

‘Inconclusive tests’

The Agentstvo report also said former US ambassador to Ukraine John Herbst, now senior director of the Atlantic Council’s Eurasia Center, suffered from poisoning symptoms a few months before Russia invaded Ukraine.

The Atlantic Council think tank confirmed Herbst showed symptoms that could be those of poisoning in April 2021 but medical tests were inconclusive.

It added that it worked with US federal investigators who took a blood sample but the lab results had failed to detect toxic compounds.

Herbst has since recovered fully, it said.

Several poison attacks have been carried out abroad and in Russia against Kremlin opponents in recent years.

Moscow denies its secret services were responsible.

But European laboratories confirmed Navalny was poisoned with Novichok, a Soviet-made nerve agent.

The nerve agent was also used in an attempted murder in 2018 of former double agent Sergei Skripal and his daughter in the English city of Salisbury.

The Skripal case further exacerbated already dire relations between London and Moscow since the 2006 radiation poisoning death in the British capital of former spy Alexander Litvinenko.