“A file has been opened based on the information available,” a Berlin police spokesman told the Sunday weekly. Berlin police were not immediately available to respond to AFP.

Russian investigative media outlet Agentstvo published an investigation this week reporting on the health problems encountered by two participants at a meeting of Russian dissidents on April 29 and 30 organized by exiled former oligarch turned Kremlin critic Mikhail Khodorkovsky.

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

The report added that the journalist went to the Charite University Hospital in Berlin — where Putin critic Alexei 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 after having had to leave Russia.

Arno was in Berlin at the end of April before traveling to Prague, where she experienced symptoms and discovered that her hotel room had been opened, Agentstvo reported.

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

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

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

Moscow denies its secret services were responsible.

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