One of Vladimir Putin's most prominent critics has been hospitalised with a mysterious "allergy" in jail.
Despite never having had a similar reaction in the past, Alexei Navalny needed medical treatment after suffering severe facial swelling.
The opposition leader is serving a 30 day sentence after calling for unauthorised protests.
He was jailed on Wednesday after calling protests claiming that anti-Putin candidates were being excluded from local elections in September.
Mr Navalny's spokeswoman Kira Yarmysh posted on Twitter : "This morning at 9.30am, Alexei Navalny was hospitalised with a diagnosis of “acute allergic reaction”: severe swelling of the face and redness of the skin.
"The source of the allergic reaction is not determined. Throughout his life, Alexei had never experienced an allergic reaction."
The homes of several of Mr Navalny's allies were also raided last week, with experts saying it is a sign the Kremlin is worried about Putin's falling approval ratings.
Mr Navalny has previously been barred from standing against the Russian President in elections.
On Saturday more than 1,300 protesters were arrested taking part in demonstrations outside Moscow City Hall.
Another of Mr Navalny's aides, Leonid Volkov, said he had been detained in the same cell last month, and suffered similar symptoms.
He wrote on Twitter: "Alexei is in the same first cell of the first joint venture in which I sat 28 days in June.
"Immediately after my release, the entire edema was covered with red spots, and I spent a week on antihistamines. Thought - an allergy.
"But apparently, Alexei has exactly the same symptoms, and this is some kind of strange allergy."
