NEW YORK—Leonard Peltier has, since the 1970s, been a symbol of the plight of hundreds of political prisoners in the United States. This courageous warrior may soon be converted from symbol to martyr if he doesn’t receive proper medical treatment immediately.

Mr. Peltier, an American Indian Movement activist, is gravely ill and near death in Leavenworth Prison in Kansas, supporters say. According to an alert from Mr. Peltier’s Defense Committee, specialists at the Mayo Clinic have offered to provide treatment without charge, either at the clinic’s facilities in Rochester, Minn., where federal prisoners are regularly treated, or at the prison itself. But the Bureau of Prisons has blocked these options, they charge.

The source of Mr. Peltier’s current condition stems in part from two botched maxilla-facial or jaw operations in a prison hospital. A member of his legal team reports that Mr. Peltier’s face is swollen beyond recognition and he can only eat by softening his food with his tongue. Over the last six months his hair has turned completely white, supporters say.

While Mr. Peltier’s jaws may have been wired tight, his pen has been moving like lightning. An event celebrating the publication of his book "Prison Writings: My Life Is My Sun Dance" occurred June 23 at Revolution Books in downtown Manhattan. Proceeds from the event went to benefit the Leonard Peltier Defense Committee.

In an attempt to absolve itself from Mr. Peltier’s plight, the Bureau of Prisons issued a statement through its web site indicating that the activist had earlier received treatment at the U.S. Medical Center for Federal Prisoners in Springfield, Mo.

"In fact, the treatment he received was horribly bungled, so that he was virtually unable to open his mouth, and for a time a wire protruded through his cheek," a press release from his Defense Committee stated. "His recovery room was a filthy and cockroach infested prison ‘hole.’ "

Like his medical treatment, the trial Mr. Peltier endured that led to his imprisonment was also a sham, his defenders add. He was charged with the shooting deaths of two FBI agents during a raid on an American Indian Movement compound at Wounded Knee, S.D., in 1975.

Mr. Peltier’s supporters have persistently proclaimed his innocence and have further charged the FBI with fabricating evidence to obtain Mr. Peltier’s extradition from Canada, where he fled following the shootout.

At the extradition hearing, the FBI presented an affidavit by a purported girlfriend of Mr. Peltier, who said that she had seen him shoot the FBI agents. However, it was later determined that the so-called girlfriend was a mental patient who had never met Mr. Peltier and was nowhere near Pine Ridge at the time of the shooting.