Punk rock icon Yegor Letov, who was once committed to a mental hospital by Soviet authorities angered by his profane and fiercely anti-Communist lyrics, has died of heart failure at age 43.

Letov died in his sleep Tuesday morning at his home in the Siberian city of Omsk, according to a brief statement on the official web site of his band, Grazhdanskaya Oborona.

Investigators from the Omsk Regional Prosecutor's Office are seeking to establish the exact cause of Letov's death, RIA-Novosti reported Wednesday. By law, the investigators have one month to issue their findings, though preliminary results could be released by the end of this week.

Citing anonymous sources, Komsomolskaya Pravda reported Wednesday that Letov's death was drawn-out and painful. The report contradicted the band's statement, which said Letov died suddenly.

The musician's funeral and a public memorial service will take place Thursday in Omsk, said Sergei Popkov, the manager of Grazhdanskaya Oborona, RIA-Novosti reported.

Letov's death marks the end of a turbulent career for one of the only Russian rock stars from the 1980s who kept his outsider status in the post-Soviet era.

He earned his controversial reputation by singing obscene songs at often rowdy concerts, by openly admitting his use of illegal drugs and by signing up with the radical, now-banned National Bolshevik Party -- a move that alienated many in the rock music community.

Letov was a "rebel without a cause," said Mikhail Kozyrev, co-founder of rock station Nashe Radio.

"He was one of those artists that was blessed with enormous talent, but this talent came with a bunch of demons that tortured him throughout his whole life, and I think he couldn't manage them," Kozyrev, who now hosts a talk show on the Silver Rain radio station, said by telephone Wednesday.

Writer Eduard Limonov, founder of the National Bolsheviks and a close friend of the late musician, described Letov as a "comrade in arms" and an "ardent revolutionary."

"He was the musical component of the party. He will not be forgotten," Limonov said, RIA-Novosti reported.

In a column he penned last year for the English-language biweekly The eXile, Limonov said the National Bolshevik flag was first unfurled at a Grazhdanskaya Oborona concert in 1993.

Letov was born in Omsk in 1964, the son of an army officer and a nurse. His name was listed as Igor in his passport, but he became known as Yegor. He never obtained a higher education.

He discovered rock as a child when his brother introduced him to the records of Shocking Blue, Led Zeppelin and the Beatles, he said in a 1989 interview posted on the Grazhdanskaya Oborona web site.

"When I heard them, they had such an effect on me that everything got going at once," he said. "I started recording rock, and I lived on this music for 10 years."

In 1982, Letov founded a band called Posev at a time when Soviet authorities were highly suspicious of the country's nascent underground rock scene. Two years later, he started Grazhdanskaya Oborona, or "Civil Defense."

Letov's lyrics were initially absurdist and apolitical, but everything changed in 1985 when authorities committed him to a mental hospital, a tactic used against especially vocal dissidents. He was kept in the hospital for three months and forced to take anti-psychotic drugs.

After he emerged in early 1986, Grazhdanskaya Oborona began to produce sharply political songs such as "Everything Is Going According to Plan," a mockery of communist optimism that became an anti-Soviet anthem and Letov's best-known song.

It contained the lyrics: "Everything will be fine under communism / It will come soon, you just have to wait / Everything will be free ... and nobody will have to die."

Forced to record in Letov's own apartment, the band eventually gained popularity in the late 1980s, and Letov became known as a Russian version of Sid Vicious, rebelling against everyone and everything.

"During the very end of Soviet rule, [our work was] an extreme provocation, full of the kind of anti-Soviet content even dissidents couldn't allow themselves," Letov recalled in an interview with The Moscow Times in 2000.

Letov remained a rebel even after the collapse of the Soviet Union. He underwent a number of political transformations and ended up as an early supporter of Limonov's National Bolsheviks, a radical group that mixed communist and nationalist ideology.

It was a combination well-suited for Letov, whose interviews with journalists were often reminiscent of his confusing, stream-of-consciousness song lyrics.

"Everybody asks me, 'Who am I? Am I a communist or not?'" Letov told The Moscow Times in 2000. "And I tell them 'I'm a communist and I'm not a communist.' When the political situation changed, I had to find a new answer."

A prolific musician, Letov recorded more than 40 albums in his two-decade career, sometimes solo but usually playing with Grazhdanskaya Oborona.

The band's recordings and live shows were full of "wild, raw, smashing energy," Kozyrev said.

"It was never a mass-audience group," he said. "It was always so raw that you would never put it on the air."

The band released its last album, "Why Do We Dream?", in May 2007. Last month, Letov said the album had sapped all his energy and that he would stop recording, news agencies reported.

At the time of his death, Letov was married to Natalya Chumakova, the bass player for Grazhdanskaya Oborona. He had no children.