The desperate underground drive to reach six trapped miners was suspended indefinitely Friday after a cave-in killed three rescuers inside a mountainside mine, a federal official said. "Is there any possible way we can continue this underground operation and provide safety for the rescue workers? At this point we don't have an answer," said Richard Stickler, head of the federal Mine Safety and Health Administration. The collapse Thursday evening killed three rescue workers and injured at least six others who were trying to tunnel through rubble to reach six miners - three of whom are from Mexico - trapped Aug. 6 inside the mountain. Stickler said mine-safety experts were being summoned to central Utah to discuss the crisis.