Russian dissident Vladimir Kara-Murza said on Tuesday that his mother was in hospital in Berlin, while German police said they were investigating a case of attempted murder.

Kara-Murza said suspicions that her mother, a Russian-German national, had been poisoned had not been confirmed.

Police said toxicology test results were not expected before Wednesday.

"My mother is indeed in a hospital in Berlin, but luckily the suspicions of poisoning or heart attack have not been confirmed," Kara-Murza posted on social media. "Doctors are continuing the evaluation."

He had complained of symptoms of intoxication

Police said the woman, whose name was not released, was being taken to the isolation wing of Charite Hospital. He had gone to the hospital in the afternoon complaining of symptoms of poisoning.

"We are currently investigating whether there is evidence of a political motivation," police spokeswoman Jane Berndt said. He added that the victim's flat, in the western district of Charlottenburg-Wilmersdorf, was being searched for leads.

Kara-Murza, a prominent critic of Russian President Vladimir Putin and his large-scale invasion of Ukraine, was one of more than 20 prisoners that Russia, Belarus and the West swapped in August, in the largest prisoner swap since the Cold War.

Among those he was traded for was Russian assassin Vadim Krasikov, convicted of the 2019 murder in a park in Berlin by a Georgian citizen who had been part of the Chechen independence movement.

Last year, Russian investigative journalist Elena Kostyuchenko fell ill on a train to Berlin after what she believed to be a poison attack. The police opened an investigation into a case of attempted murder.