The wife of stricken Kremlin critic Alexei Navalny appealed to President Vladimir Putin on Friday to allow the opposition politician to be flown to Germany for urgent medical care from a hospital in Siberia.
Navalny, a foe of Putin and his lieutenants and a campaingner against corruption, is in serious condition after drinking tea on Thursday morning that his allies believe was laced with poison.
His condition improved a little overnight but his life was still in danger and he was not well enough to be moved from the hospital, doctors treating him in Omsk, Siberia, said.
German doctors flew into the city in an air ambulance sent by the Berlin-based Cinema for Peace Foundation, a non-profit organisation, with the intention of flying him to Germany if possible.
Alexander Murakhovsky, the head doctor at the hospital, said Navalny had been diagnosed with a metabolic disease that may have been caused by low blood sugar.
He said traces of industrial chemical substances had been found on the 44-year-old's clothes and fingers hours and that doctors did not believe Navalny had been poisoned.
Navalny's wife Yulia and his spokeswoman Kira Yarmysh, who want to fly Navalny to Germany for medical treatment, have criticised the hospital after it said that moving him would put his life at risk because he was still in a coma and his condition unstable.
Yulia Navalnaya sent a letter to the Kremlin directly appealing for it to intervene, Navalny's supporters said.
"I officially appeal to you (Putin) to demand you allow the transportation of... Navalny to .. Germany," the letter published on social media said.
Yarmysh said doctors had previously consented to his being moved, but had withheld their agreement at the last minute.
"The ban on transporting Navalny is an attempt on his life being carried out right now by doctors and the deceitful authorities that have authorised it," Yarmysh wrote on Twitter.
"This decision, of course, was not made by them, but by the Kremlin," she said.
Speaking before the letter was sent, the Kremlin said on Friday it was up to doctors to decide whether Navalny was fit to be moved from the hospital and that it had not received any formal request to help.
Murakhovsky told reporters that many legal questions would need to be resolved before Navalny could be handed over to European doctors.
He said top doctors had been flown in from Moscow to treat Navalny who were no worse than their European counterparts. Test results would be available within two days, he said.
Navalny fell ill while on a flight and he was stretchered off the plane and rushed to hosipital after it made an emergency landing in Omsk.
Navalny has been the biggest thorn in the Kremlin's side for more than a decade, exposing what he says is high-level graft and mobilising crowds of young protesters.
He has been repeatedly detained for organising public meetings and rallies and sued over his investigations into corruption. He was barred from running in a presidential election in 2018.
Navalny's team cited a police officer as saying a highly dangerous substance had been identified in his body that posed a risk to everyone around him and that they should wear protective suits. Reuters could not independently confirm that information.
Navalny's team said it believed authorities wanted to stall for time so that any trace of what poisoned him would disappear.