Los Angeles (CNN) -- A three-week hunger strike by some California prison inmates has ended, the Department of Corrections said Thursday.
More than 4,250 inmates in eight state prisons were involved in the strike on September 29, three days after it began, but only 580 at three prisons were still participating Thursday, the department said in a news release.
On October 6, when the department said 811 were still taking part, Jay Donahue, a spokesman for Prisoner Hunger Strike Solidarity, questioned that number, though he acknowledged that participation had likely dropped.
Prison officials consider inmates to be on a hunger strike if they have missed nine straight meals.
The Corrections Department said Thursday it had received a letter from inmates two days earlier regarding the strike. The letter was the first contact from the striking inmates or their representatives, it said.
"Officials agreed to meet with inmate representatives to discuss its ongoing review of and revisions to its Security Housing Unit policies that began in May 2011," the department said in its news release. "Similar to its discussions with inmates during a July hunger strike, all agreed the changes to policies would take several months to finalize. The department agreed to continue on its same course."
Many of the inmates were angry about a practice of keeping them in solitary confinement for too long, some as many as 20 years, Isaac Ontiveros, another spokesman for Prisoner Hunger Strike Solidarity, said earlier.
The prisoners made five demands, including a change in the policy that makes inmates go through an interrogation process in which they have to incriminate themselves -- and identify other inmates who are involved in breaking rules -- in order to get out of solitary confinement. They also demanded an end to group lockdowns and wanted more privileges for those in solitary confinement, such as winter clothes and nutritious meals.
Prison officials have said that placing prisoners in segregation units, or solitary confinement, in the Security Housing Unit makes the facilities safer and helps guards deal with gang violence.
The department said it is looking into reports of threats or retaliation against inmates who refused to participate in the hunger strike.
There are approximately 160,355 inmates in the state's 33 prisons, 42 conservation camps, community-based correctional facilities and three out-of-state contract facilities, the department said.
CNN's Stella Chan contributed to this report