NEW YORK, AUG. 22 -- An inmate's stabbing touched off the second uprising in eight days at the city's Rikers Island jail and left about 25 guards and four prisoners injured, authorities said today.

Eighteen inmates barricaded themselves in their cellblock and set fires Tuesday night after the prisoner was stabbed, said Correction Department spokeswoman Ruby Ryles. The assailant's identity was not known, she said.

Forty guards ended the uprising within 30 minutes, Ryles said. It was not immediately known if force was used.

Ryles had said Tuesday night that about 75 people were injured and that most of them were treated for smoke inhalation. None of the injuries was life-threatening, Ryles said. Twenty-five guards and four inmates were taken to local hospitals, Emergency Medical Services spokeswoman Gail Christianson said today.

Last week, up to 1,000 guards blockaded the entrance to the island in the East River for 36 hours, protesting inmate violence against guards and demanding more authority to use force.

The blockade left the jail short of staff and prevented inmates from receiving visitors. As the blockade was ending Aug. 14, hundreds of prisoners rioted in anger, and 162 guards and inmates were reported injured, most of them by tear gas.

During the disturbance, officers were accused of lining up some inmates and beating them with nightsticks. The city is investigating.

The blockade ended after guards reached an agreement that allowed greater leeway in use of force. But a federal judge barred implementation of the new rules and ordered a compromise be reached.