Russian doctors have been denied access to ailing opposition politician Alexei Navalny at the prison camp where he is being detained to the east of Moscow.
"Who do you have to be to deny doctors access to a dying person?" Navalny's doctor Anastasiya Vasilyeva said on Tuesday outside the camp in Pokrov about 100 kilometres east of Moscow.
There, medics from the independent union Alliance of Doctors wanted to help the political prisoner.
Vasilyeva and others were arrested and put in prison vans, union said.
Navalny is said to have severe back pain and paralysis in his leg, a fever and cough.
He accuses the penal system of torture and has gone on hunger strike to protest inadequate medical care.
Human rights campaigners Amnesty International called on President Vladimir Putin not to let his opponent die.
The Alliance of Doctors criticised the fact that Navalny, who narrowly survived an assassination attempt with the nerve agent Novichok in the summer, was not receiving adequate medical care.
CNN's Moscow correspondent Matthew Chance also posted a photo on Twitter of his temporary detention.
The Foreign Ministry in Moscow said that journalists had obstructed work outside the detention centre. Chance and his team were released after a few hours.
Russian state propaganda had recently compared the prison camp to a sanatorium, a holiday camp and a hotel.
Moscow rejects international calls for the 44-year-old's immediate release.
"If it really is an illness, then treatment will be ensured at the appropriate, designated level," Kremlin spokesman Dmitry Peskov said according to the state news agency TASS.