Dr. John Brown, an emergency room physician at the hospital, said the tiger inflicted deep bites and claw cuts to the injured men's heads and upper bodies, the San Francisco Chronicle reported. Officials said the men, whose injuries were first considered life-threatening, were able to talk about the attack Tuesday and could soon be released.

Zookeepers said they haven't determined how the tiger, a 4-year-old named Tatiana, was able to escape from the grotto where the tigers are kept. They said the tiger, which injured a keeper during an attack in December 2006, didn't go through the grotto's only door.

"We don't know how it was able to get out," said Robert Jenkins, director of animal care at the zoo. "The tiger should not have been able to jump (out). This is the first thing we will be investigating."

Police said they haven't ruled out carelessness or criminal activity as causes of the escape.

The animal was shot and killed by police officers at the zoo.