Inmates at a "maxi-maxi" prison for New York's toughest convicts were able to riot and take hostages because guards abandoned their posts to eat lunch, the state's prison chief said.

Corrections Commissioner Thomas Coughlin blamed this "serious breach of security protocol," more than the policy of housing hundreds of unruly inmates in one facility. That policy was criticized after the uprising May 28 at Southport prison near Elmira in upstate New York.Coughlin issued a report Sunday that said seven guards went inside to eat lunch, leaving inmates unsupervised in recreation pens outside.

"At one point, there were no officers in the yard at all. . . . An incident of serious magnitude could - and, in fact did - take place without being detected," the report said.

Prison guards do not get a lunch break and are supposed to eat at their posts.

Fifty-three inmates took five guards hostage during the 25-hour standoff. No one was killed, but one guard was seriously injured.

Coughlin was scheduled to testify Monday at a state Commission of Corrections hearing on the riot. A representative of Council 82, the prison guards' union, also was to testify.

Council 82 said in a statement Sunday that the report "reveals the usual state effort to blame its employees and their unions for the blunders and tragedies caused by its own mismanagement."