A leading anti-government protester in Ukraine has reappeared eight days after going missing, claiming he was abducted and "crucified".

Dmytro Bulatov, 35, one of the leaders of anti-government protest motorcades called "automaidan", turned up on Thursday (local time) with his face badly beaten and with wounds to his hands.

He has told a Ukraine television station that during a week of being confined, he was tortured by his kidnappers.

It comes as the UN High Commissioner for Human Rights is calling for an investigation into claims of torture in Ukraine.

Mr Bulatov says he feels lucky to be alive.

"I was crucified. I've got holes in my hands," he said.

"A part of my ear was cut off. They cut my face. There's not a spot on my body that hasn't been beaten.

"I couldn't tell who they were as it was always dark where they kept me but their accent was Russian."

Mr Bulatov's disfigured and swollen face was replayed on TV screens throughout the day.

Ukrainian opposition leaders rushed to the hospital, after police went there in what the opposition said was a move to arrest Mr Bulatov.

Mr Bulatov is on a police wanted list on suspicion of taking part in "mass disorder", which carries a sentence of up to eight years in jail.

Police said they went to the Kiev clinic where Mr Bulatov was being treated for his injuries but have since left after medical staff denied them access to Mr Bulatov.

Opposition leaders, including boxer-turned-politician Vitaly Klitschko, said that police had intended to arrest him but had been thwarted by doctors who quickly called opposition leaders to the scene.

"The police are trying to provoke further escalation of the conflict and increase tension in society. Instead of searching for those guilty for the disappearance and torture of one of the leaders of the automaidan," Mr Klitschko's UDAR (Punch) Party said in a statement.

"The police are trying to make a criminal of him."

Another opposition leader, far-right nationalist Oleh Tyahnibok, told reporters attempts to arrest Mr Bulatov had been thwarted by the quick response of doctors.

He said opposition deputies would take shifts overnight to protect Mr Bulatov from the police.

Bulatov organised automaidan protest on president's residence

Mr Bulatov was reported missing on January 23.

He was involved in several motorcade protests, in which scores of cars would drive to the homes of Ukrainian leaders. Automaidan is a word play on Maidan, the Kiev square that is a focus for revolt.

In the biggest motorised protest, about 2,000 cars drove to the country residence of president Viktor Yanukovych at Mezhyhirya, outside Kiev, on December 29.

They came within 300 metres of his residence before being stopped by security roadblocks.

Traffic police have begun to try to identify participants in the protests, and protest groups say about 20 people so far have been detained for questioning.

In Brussels, European Union foreign policy chief Catherine Ashton said she was appalled by signs of torture inflicted on Mr Bulatov.

"All such acts are unacceptable and must immediately be stopped," she said in a statement.

News of Mr Bulatov's kidnapping and injuries emerged ahead of another weekend of protest rallies in Kiev, though organisers have discouraged people from turning out because of a cold spell that has sent night temperatures plunging to minus 18 degrees Celsius.

The protests began after Mr Yanukovich rejected an EU trade deal last November in favour of closer ties with Moscow and a financial bailout from Russia.

They have since spiralled into a public show of anger against perceived misrule and corruption.

US secretary of state John Kerry is urging Mr Yanukovych to offer more reforms or risk uncontrollable violence.

Mr Kerry says the concessions offered so far do not go far enough to satisfy the demands of the protesters and warned continued violence is in the interests of no-one.