By Andrius Sytas

VILNIUS, Feb 6 (Reuters) - A Ukrainian anti-government activist who fled the country after being abducted said on Thursday he had been forced under torture to declare himself an American spy.

Dmytro Bulatov, leader of a protest group known as Automaidan, said his kidnappers forced him to say on camera that he had accepted money from the U.S. Embassy to organise anti-government protests in Ukraine.

"I was telling them lies just to stop the torture... At one point I asked them to kill me because I couldn't stand it any more," said the 35-year-old, speaking at the Vilnius University Emergency Hospital in Lithuania where he is being treated after leaving Ukraine on Sunday.

Bulatov, was found bloodied and injured in woods outside Kiev on January 30. He said unidentified assailants had driven nails through his hands in a "crucifixion" and had beaten him during a week in captivity.

EU leaders offered to help the activist after Ukrainian police said they wanted to charge him with taking part in "mass disorder" related to protests consisting of convoys of sometimes hundreds of cars driving up to the homes of allies of Ukrainian President Viktor Yanukovich.

Bulatov described his kidnap as "the worst experience I've ever had". He still suffered severe headaches and dizziness.

Video of his bloodied face has been replayed repeatedly on opposition television channels in Ukraine, fuelling anger among protesters occupying main streets and public buildings across the country.

Bulatov said he would not return to Ukraine unless he got guarantees that he will not be prosecuted.

"I want my government to give guarantees to the international community that I will not be politically prosecuted," he said later, speaking with Reuters.

"The government should close all criminal cases against activists, including me, who have taken part in the protests."

Yanukovich sparked the protests in November when he spurned a trade pact with the 28-nation EU and turned instead to Ukraine's old master Moscow for financial support. (Writing by Nerijus Adomaitis, Editing by Jack Stubbs and Ralph Boulton)