Dmytro Bulatov, 35, one of the leaders of anti-government protest motorcades called Automaidan, speaks to journalists after being found near Kiev, in a still image from footage obtained by Reuters TV, Jan. 30, 2014.

A Ukrainian anti-government activist who disappeared a week ago during widespread protests in and around Kiev has resurfaced with his face badly beaten and with wounds to his hands, saying his abductors tortured and "crucified" him.

Police have opened an investigation into the kidnapping of Dmytro Bulatov, 35, who was one of the leaders of anti-government protest motorcades called Automaidan. He was discovered outside Kiev on Thursday, and appeared on Ukrainian TV station Channel 5 Friday.

"They crucified me, they nailed down my hands. They cut off my ear, they cut my face. There isn't a spot on my body that hasn't been beaten," Bulatov said.

"Thank God, I am alive."

He also said he was kept in the dark at all times, and could not identify his captors.

At least seven people are known to have died during unrest that has dogged the country for weeks.

The spokesman for the United Nations High Commissioner for Human Rights, Rupert Colville, called for an investigation into claims of torture and kidnappings in Ukraine.

In a statement Friday the U.N. said it was "appalled by the deaths reported in recent days in Kiev."

Bulatov was reported missing on Jan. 23. He was involved in several motorcade protests in which scores of cars would drive to the homes of Ukrainian leaders.

In the biggest such protest, about 2,000 cars drove to the country residence of President Viktor Yanukovich in Mezhyhirya, outside Kiev, on Dec. 29. They came close to his residence before being stopped by security roadblocks.

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

Oleksiy Hrytsenko, Bulatov's friend and fellow activist, said Automaidan members had come under tremendous pressure during the protests, with their cars burnt and activists arrested, harassed and threatened.

He showed an Associated Press reporter a text message he had received from an unknown number that read: "Go ahead, go ahead, your mother will be happy to see her son dead."

Bulatov is among three activists whose disappearances have shocked the country, especially after one of them was found dead.

Bulatov went missing one day after Igor Lutsenko, another prominent opposition activist who had also gone missing, was discovered after being taken to the woods and beaten severely by unknown attackers.

Lutsenko was kidnapped from a hospital, where he had brought a fellow protester, Yuri Verbitsky, to be treated for an eye injury. Verbitsky was also beaten severely and was later discovered dead.

Opposition leader Vitaly Klitschko, who visited Bulatov in the hospital, said, "What was done to Dmytro was an act to frighten all citizens who are being active now."

Bulatov's reappearance came two days after the prime minister, Mykola Azarov, offered his resignation in a bid to ease the two-month crisis.