Expert: Wary of quickly ruling out Navalny poisoning

A UK toxicology expert said he would want "more than a second opinion" on the ruling out of poison as the cause of Russian opposition leader Alexei Navalny's serious illness which has left him in a coma in hospital.

Navalny, one of Vladimir Putin's fiercest critics, lay in a coma on Friday at a Siberian hospital after falling ill on flight back to Moscow from the city of Tomsk.

His supporters are calling the incident a suspected poisoning that they believe was engineered by the Kremlin.

Omsk hospital deputy chief doctor, Anatoly Kalinichenko, said that no traces of poison were found in the politician's body and doctors didn't “believe the patient suffered from poisoning.”

Professor Alastair Hay, a toxicology expert at the University of Leeds, said he would be wary of ruling out poisoning too soon.

"It takes a while to rule things out and particularly if something is highly toxic, it will be there in very low concentrations, and many screening tests would just not pick that substance up," he said.

"A blanket ruling out within 24 hours, well I would be, I would want more than a second opinion on that."

Hay said due to the seriousness of Navalny's condition the family's doctors should also be able to have access to him as "you want as many brains as possible" to help treat him.

A plane with German specialists and all the necessary equipment landed at Omsk airport on Friday morning, prepared to take Navalny to a top clinic in Berlin.

But doctors at the hospital said his condition was too unstable to transport him.

After much wrangling, German doctors were being allowed access to him, an associate said

Like many other opposition politicians in Russia, Navalny has been frequently detained by law enforcement and harassed by pro-Kremlin groups.

In 2017, he was attacked by several men who threw antiseptic in his face, damaging an eye.