An Oklahoma Indian tribe says an embattled University of Colorado (search) professor whose claim of Indian heritage is under investigation "could not prove any Cherokee ancestry."

In a statement on its Web site, the United Keetoowah Band of Cherokee Indians (search) said it gave Ward Churchill (search) an "honorary associate membership" because he promised to write a tribal history.

Churchill, a tenured professor of ethnic studies who could lose his job over allegations that he lied about his ancestry and plagiarized others' work, said Wednesday the tribe's statements are false.

In an e-mail to The Associated Press, Churchill said the United Keetowahs' membership committee twice confirmed he has Cherokee ancestors before he was made an associate member. He said the tribe has a right to disenroll him or ask him to resign, but that it hasn't done so.

Churchill touched off a firestorm when he wrote an essay comparing some of the World Trade Center victims to Adolf Eichmann (search), one of the Nazis who orchestrated the Holocaust. CU leaders said he couldn't be fired over the statements because of First Amendment protections, but they ordered a faculty panel to review the allegations of plagiarism and that he falsely claimed to be an Indian to give his research more credibility.

Besides insisting on his Indian heritage, Churchill has denied plagiarism.

The Keetoowah statement, first reported by the Rocky Mountain News (search), said the tribe "has no association with Churchill in any capacity whatsoever" and called his comments about the Sept. 11 victims offensive.

A tribal spokeswoman did not immediately return a message Wednesday seeking further comment.

Churchill's essay called some of the Trade Center victims "little Eichmanns" in an apparent reference to their work on behalf of a U.S. government he contends is an oppressive economic empire.

He has refused to retract the statement but said he wishes he had phrased it differently.