• Alexei Navalny was dispatched to fly him to Germany for treatment, with an air ambulance on its way to pick up the Russian opposition figure are a suspected poisoning.
• An air ambulance left Nuremberg early on Friday to collect Navalny after Chancellor Angela Merkel extended an offer of treatment.
• The 44-year-old leader was hospitalised in the city of Omsk after he lost consciousness while on a flight and his plane made an emergency landing.

Russian doctors say Kremlin critic Alexei Navalny cannot be moved from the Siberian hospital where he is being treated for suspected poisoning, putting his life at risk, his spokesperson said on Friday.

"The chief doctor stated that Navalny is not transportable. Condition is unstable," Kira Yarmysh said on Twitter.

"The ban on transporting Alexei is a direct threat to his life. It is deadly to remain in the Omsk hospital without equipment or a diagnosis."

Yarmysh said an air ambulance dispatched to fly him to Germany for treatment was due to land shortly.

"The ban on the transportation of Navalny is an attempt on his life, which is being made right now by doctors and the deceitful authorities who sanctioned it."

An air ambulance left Germany on Friday morning on its way to pick up Russian opposition figure Alexei Navalny from hospital in Siberia, German media reported.

The rescue aircraft was dispatched from the Bavarian city of Nuremberg at 03:11, the Bild daily reported.

The head of a German NGO had earlier told AFP that Berlin's Charite hospital was ready to treat Navalny, who is fighting for his life after a suspected poisoning.

The leading Russian opposition figure, a 44-year-old lawyer and anti-corruption campaigner who is among President Vladimir Putin's fiercest critics, was hospitalised in the city of Omsk after he lost consciousness while on a flight and his plane made an emergency landing.

"The doctors are really working now on saving his life," the hospital's deputy head doctor Anatoly Kalinichenko told journalists in Omsk.

Navalny's spokesperson Kira Yarmysh said he was on a ventilator in a coma and his condition was serious but stable.

"Alexei has toxic poisoning," Yarmysh wrote on Twitter, describing how he was taken ill during the flight from the city of Tomsk to Moscow.

The hospital has not released any diagnosis while the regional health ministry said Navalny's coma was not medically induced.

An air ambulance left Nuremberg early on Friday to collect Navalny after Chancellor Angela Merkel extended an offer of treatment, German media reported.

"I hope that he can recover and... he can receive from us all the help and medical support needed," Merkel said in a joint news conference with French President Emmanuel Macron.

Navalny's team had said earlier that the hospital in Omsk was ill-equipped and his doctor Anastasia Vasilyeva said she had asked for the Kremlin's help to transfer him to a European clinic.

Putin's spokesperson Dmitry Peskov wished Navalny a "speedy recovery" after pledging Kremlin help to secure him treatment abroad if needed.

Peskov said claims of poisoning were "only assumptions" until tests proved otherwise.

Yarmysh claimed Putin was responsible for poisoning Navalny, saying: "Whether or not he gave the order personally, the blame lies with him."

'Something in his tea'

Navalny's wife Yulia travelled to visit him in the city about 2 200 kilometres east of Moscow.

Yarmysh said police and investigators had also arrived and journalists reported seeing FSB security service agents at the hospital.

"We think that Alexei was poisoned with something mixed in his tea. That was the only thing he drank in the morning," Yarmysh wrote on Twitter.

She told the Echo of Moscow radio station that she was "sure it was intentional poisoning".

State news agency TASS cited a sceptical response from a law enforcement source.

"We can't rule out that he drank or took something himself yesterday," the source said, a claim Yarmysh dismissed as "complete rubbish".

She said that Navalny seemed "absolutely fine" when they went to Tomsk airport.

"Straight after take-off he quite quickly lost consciousness."

Political analyst Tatiana Stanovaya said that Navalny had "hundreds of enemies including some hardened individuals", pointing to his anti-corruption investigations that attract millions of views online.

Amnesty International urged Russia to hold a "prompt and independent investigation" into the incident while European Union foreign affairs chief Josep Borrell said "those responsible must be held to account" if the suspected poisoning was confirmed.

Muscovites said they suspected Navalny was poisoned over his political views.

"I think this is a deliberate attempt on his life because he has fought so fiercely with the government lately," said 18-year-old student Yaroslav Lyangasov.

Previous attacks

Navalny has suffered physical attacks in the past, including a 2017 incident where he endured chemical burns to his eye after green dye was splashed on his face.

Last year Navalny said he suspected poisoning when he suffered rashes and his face became swollen while serving a short jail term after calling for illegal protests.

A charismatic lawyer and whistleblower, Navalny has been travelling the country to promote a tactical voting strategy to oppose pro-Putin candidates in regional elections in September.

Navalny went to Siberia to help opposition candidates.

He has been the target of multiple criminal probes and spent numerous stretches in police cells for organising illegal protests, while his Anti-Corruption Foundation is regularly raided by police and investigators.

Thursday's incident follows several infamous poisonings of Kremlin critics in the past.

Britain named two Russian spies as suspects after Russian double agent Sergei Skripal and his daughter Yulia were poisoned with the nerve agent Novichok in the city of Salisbury in March 2018.

Former Russian security service agent Alexander Litvinenko was fatally poisoned with radioactive polonium in a cup of tea in London. Russia refused to extradite chief suspect Andrei Lugovoi, who became a nationalist MP after the 2006 attack.

Several other opposition figures have suffered severe illnesses in Russia that they blamed on poisoning.