LOS ANGELES (Reuters) - Supporters of California prison inmates staging a prolonged hunger strike said on Saturday that one of the prisoners who had been refusing meals has died, but state corrections officials said the death was under investigation as a suicide. The inmate, identified by mediators for protesting inmates as Billy Sell, died on Monday at the Corcoran State Prison in central California, where he was serving time in a 'security housing unit' for prisoners held in solitary confinement, according to the Prisoner Hunger Strike Solidarity Coalition

LOS ANGELES (Reuters) - Supporters of California prison inmates staging a prolonged hunger strike said on Saturday that one of the prisoners who had been refusing meals has died, but state corrections officials said the death was under investigation as a suicide.

The inmate, identified by mediators for protesting inmates as Billy Sell, died on Monday at the Corcoran State Prison in central California, where he was serving time in a "security housing unit" for prisoners held in solitary confinement, according to the Prisoner Hunger Strike Solidarity Coalition.

The group said in a statement that fellow inmates have reported that Sell was participating in the hunger strike, and that he had been requesting medical attention for several days before his death.

The hunger strike, which entered its 20th day on Saturday, was launched in protest against the state's solitary confinement practices and ranks as the largest in California prison history.

"Advocates are outraged at Sell's death, noting that it could have been prevented if (prison officials) had negotiated with strikers," the coalition said in its statement.

The California Department of Corrections and Rehabilitation disputed those assertions.

"It's irresponsible and inflammatory for hunger strike supporters to say this inmate, whose death is being investigated as a suicide, died as a result of the hunger strike," the department spokeswoman Deborah Hoffman said in a statement.

She added, "The inmate was not participating in the hunger strike at the time of this death."

The statement gave no further details about the circumstances of his death, except to say that the 32-year-old inmate was found "unresponsive" in his cell on July 22 and was pronounced dead at the prison's hospital that night.

"Also, because it is the weekend, I cannot tell you if the autopsy has been completed," she said.

According to Hoffman, the inmate was serving a life term for attempted murder and was awaiting trial in connection with the 2007 slaying of a cell mate at Corcoran.

Corrections officials did not immediately respond to requests for additional information about the death or the investigation.

Thousands of inmates in high-security lockups throughout the state launched the hunger strike on July 8 to protest what advocates say is the unfair and inhumane use of solitary confinement as punishment within the system.

Supporters of the striking inmates say more than 30,000 of California's 132,800 inmates have taken part in the action.

Prison officials say the number of inmates who have continued to decline at least nine consecutive meals - the minimum number that they say qualifies as a hunger strike - has dwindled to 601 inmates in nine prisons as of Saturday.

The state has 4,527 inmates held in security housing units, some for committing crimes while incarcerated and others who have been identified as gang members, according to prison officials.

Inmate advocates put the number of state prisoners confined in extreme isolation at nearly 12,000.

According to the Los Angeles Times, prison infirmaries have treated six hunger-striking inmates for conditions such as dehydration, dizziness and disorientation, and more than a dozen additional prisoners have lost 10 percent or more of their body weight from refusing meals.

There has been no indication from either side in the dispute that any inmate has faced the prospect of being force-fed. (Additional reporting by Sharon Bernstein; Editing by Mohammad Zargham)