LANCASTER, Calif. (NNPA)—Attorneys for the NAACP Legal Defense & Educational Fund are calling a month-long denial of visitors for Black inmates "totally unconstitutional."

The policy has raised concerns about discrimination and civil rights violations, but officials at Lancaster State Prison said allowing prisoner visits would hamper their investigation into the bloody August attacks on three prison guards.

Visitation rights for more than 300 Black inmates were halted Aug. 12 after the attack on the guards, including one who was stabbed in the head, officials said.

Lt. Ron Nipper, a prison spokesman, said only Black inmates in one cellblock were being kept from having visitors and mingling with the prison population because suspects in the attack were believed to be Black. Two Black prisoners may face charges of attempted murder in connection with the attack, he said

Authorities are searching for an undisclosed number of other Black suspects and allowing the inmates more freedom would hamper the investigation, Lt. Nipper said.

As in many circumstances related to keeping order in prisons, the ongoing investigation requires isolating the inmates for the time being, Lt. Nipper said.

But some civil rights advocates and legal experts said although courts often give prisons much leeway in dealing with inmates, applying restrictions based on race raises concerns about constitutional rights.

Miriam Gohara, an attorney with the NAACP Legal Defense and Educational Fund, called the practice "totally unconstitutional."

Russ Heimerich, a California Department of Corrections spokesman, said that such race-based restrictions are not uncommon in state prisons. He added that many prisoners fraternize only with members of their own race, often forming race-based gangs.

As a result, he said, the distinction between a restriction aimed at a particular gang—as opposed to one aimed at a particular race—can be hazy. Mr. Heimerich said the safety of prison guards is paramount.

Authorities said that like many state prisons, the Lancaster facility, located in the Mojave Desert about 70 miles north of downtown Los Angeles, is severely crowded.

Built in 1993 to house about 2,200 inmates, the prison now has about 4,000. The inmate population is 39 percent Black, 28 percent Latino and 25 percent White, with six percent of inmates of other ethnic backgrounds.