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The BBC's Duncan Crawford reports how Bulatov claims he was beaten and hung up by his wrists
A leading activist in Ukraine's street opposition who vanished for eight days says he was abducted and tortured before being left to die in the cold.
Dmytro Bulatov, who organised car protests for the opposition camped out in Kiev, is being treated in hospital after being found near the capital.
Police have confirmed Mr Bulatov, 35, received an ear injury and bruising.
In another development, the army called on President Viktor Yanukovych to take "urgent steps" to ease the crisis.
Three protesters and three police officers have been killed, and scores injured on both sides, since the protests turned violent on 22 January.
Dmytro Bulatov
- One of the leaders of AutoMaidan, a group of drivers associated with the anti-government protests
- The group have reportedly used their cars to pick up protesters, picket properties belonging to government officials and, allegedly, block streets to police
- Mr Bulatov reportedly took to the stage in Independence Square, focus of the protests, on several occasions
- He vanished on 22 January, only reappearing again on 30 January, injured and saying he had been kidnapped, tortured and finally dumped from a car near Kiev
Opposition to Mr Yanukovych spilled into the streets in November after he abandoned a trade deal with the EU in favour of closer economic ties with Russia.
Mr Yanukovych accused the opposition of seeking to "inflame" the situation on Thursday by continuing the protests despite moves by the government and parliament to ease the stand-off.
Parliament voted to annul a recently enacted law restricting protests and passed a law giving amnesty to detained protesters, under the condition that occupied buildings were vacated.
Anti-government demonstrators remain in their camp in Independence Square (Maidan) with no sign of the political crisis in the country coming to an end, the BBC's Duncan Crawford reports from Kiev.
Mr Yanukovych, 63, has gone on sick leave, with his staff reporting he has a respiratory illness and a high fever.
'Crucified'Mr Bulatov says he was left to die by his captors after being kidnapped, repeatedly beaten and "crucified". He was, he said, hung up by his wrists.
"They crucified me, so there are holes in my hands now," he said.
"Other than that - they cut off my ear, cut up my face. My whole body is a mess. You can see everything. I am alive. Thank God for this."
The activist reportedly said he did not know who had abducted him but his abductors had spoken with Russian accents.
According to the Ukrainian news website Gazeta.ua, doctors found no damage to his internal organs or his skull.
Police in Kiev have confirmed Mr Bulatov was bruised and received a cut to one of his ears, Ukrainian newspaper Ukrainskaya Pravda reports.
They have opened an investigation and posted guards at the hospital where he is being treated.
According to the paper, they also expressed indignation that Mr Bulatov had not phoned them after his release.
Ukraine unrest - key dates
21 Nov 2013: Ukraine announces it will not sign a deal aimed at strengthening ties with the EU
30 Nov: Riot police detain dozens of anti-government protesters in a violent crackdown in Kiev
17 Dec: Russia agrees to buy $15bn of Ukrainian government bonds and slash the price of gas it sells to the country
16 Jan 2014: Parliament passes law restricting the right to protest
22 Jan: Two protesters die from bullet wounds during clashes with police in Kiev; protests spread across many cities
25 Jan: President Yanukovych offers senior jobs to the opposition, including that of prime minister, but these are rejected
28 Jan: Parliament votes to annul protest law and President Yanukovych accepts resignation of PM and cabinet
29 Jan: Parliament passes amnesty law for detained protesters, under the condition occupied buildings are vacated
Mr Bulatov is a prominent anti-government activist as one of the leaders of the organisation Automaidan, a group that has patrolled streets around Independence Square, our correspondent says.
It has also driven in convoys to protest outside government ministers' homes.
Vitali Klitschko, one of the most prominent leaders of the protesters, visited Mr Bulatov in hospital.
Offers rejectedUkraine's defence ministry put out a statement after Defence Minister Pavlo Lebedyev met staff in Kiev.
"Laying out their civil position, servicemen and employees of Ukraine's armed forces... called on the commander-in-chief to take urgent steps within the limits of existing legislation with a view to stabilising the situation in the country and reaching consent in society," it said.
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Matthew Price compares life inside the "protest zone" in Kiev with the rest of the city, where life continues as normal
Soldiers have not been deployed against the protesters during the crisis, which has seen government buildings occupied.
President Yanukovych accepted the resignation of Prime Minister Mykola Azarov and his cabinet this week, and offered senior jobs to the opposition - offers that were rejected.
Demonstrators accuse the security forces of being behind the abductions and brutality towards protesters.
Of the other two activists abducted this month, one was found dead in a forest near Kiev with his body reportedly showing signs of torture.
The activist, Yuri Verbitsky, was reportedly abducted along with fellow protester Igor Lutsenko, who was later released and spoke about his ordeal.