She said one vehicle used by authorities was hit by a bullet.

However, no one was hurt, said Reinaldo Rangel, a national prisons administrator.

Some of the inmates' relatives outside the prison hurled rocks and other objects at the National Guard troops, who responded by using tear gas. Firefighters said at least eight people received medical help after inhaling tear gas.

Maria Escobar, whose brother is imprisoned, said relatives were rightly protesting out of concern that there could be clashes involving inmates and troops.

"If they go in there like this, there's going to be massacre," Escobar said.

The gunfire eventually died down, and Varela said the authorities would keep talking with the inmates to convince them to leave voluntarily and be transferred to other prisons.

She said that La Planta is unfit to hold "any human being."

Tensions have grown at the prison recently after what the authorities said were escape attempts.