Top opposition leader returned to prison after treatment for what was described as an ‘allergic reaction’.

Alexei Navalny‘s personal doctor has said the jailed Russian opposition leader was discharged from a Moscow hospital after a possible exposure to an unidentified “toxic agent”, while health officials insisted his condition was satisfactory.

Anastasia Vasilyeva, the 43-year-old’s physician, told Russia’s Dozhd broadcaster that Navalny was returned to the prison on Monday.

“We cannot rule out that toxic damage to the skin and mucous membranes by an unknown chemical substance was inflicted with the help of a ‘third party’,” Vasilyeva earlier wrote on Facebook.

After she was allowed to visit Navalny on Monday, Vasilyeva said in a separate Facebook post that the patient’s condition had improved after intensive treatment with steroid medication prednisolone.

On Sunday, Russian President Vladimir Putin‘s top opponent was taken to Moscow’s hospital No 64 for what authorities described as an “allergic reaction” while serving a 30-day jail sentence for violating protest laws.

A hospital representative told AFP news agency on Monday that Navalny was “in a satisfactory condition”.

“His body temperature is 36.6C,” the representative said, declining to release Navalny’s precise diagnosis.

Prominent opposition figure

Vasilyeva, who said Navalny had a rash on his upper body, skin lesions, and discharge from his eye, called for samples of the 43-year-old’s bedsheets, skin and hair to be tested for chemicals.

Vasilyeva, who treated Navalny in 2017 when he nearly lost the sight in one eye after an attack, accused the doctors of not wanting to investigate what had caused Navalny’s illness.

They say “he simply has hives. But why are you lying?” the ophthalmologist said. “They have decided against establishing the cause of generalised oedema and rash,” she said.

Separately, Navalny’s lawyer, Olga Mikhailova, told reporters in front of the hospital on Monday that her client had been poisoned by an undentified chemical agent.

Al Jazeera’s Imran Khan, reporting from Moscow, said Navalny’s lawyer was given access to her client, but only after an argument with the hospital.

“They were not allowed to meet in private,” he said, adding that Navalny’s condition “is said to be stable”.

Khan said Navalny was “a very key figure” in Russia’s opposition, adding that “anything that happens to this man really concerns” anti-government activists.

The Putin critic is serving a 30-day jail sentence for calling a mass protest after authorities blocked prominent opposition candidates from taking part in Moscow city elections in September.

Navalny’s hospitalisation came a day after almost 1,400 people were arrested at the demonstration the opposition leader had called.