SACRAMENTO — A 12-year-old boy has been arrested on suspicion of arson after authorities said they believed he set his 13-year-old friend on fire Wednesday.

The 13-year-old suffered severe burns to his legs and less severe burns to his arms and abdomen. Firefighters treated and transported the boy to to UC Davis Medical Center. His condition was not immediately known.

Earlier reports had investigators checking if some teens had set the boy on fire or if he had set himself on fire.

The incident happened about 2 p.m. in Sacramento, investigators said.

The boys were playing with rubber balloons filled with lighter fluid when one of the balloons broke and soaked the 13-year-old, Sacramento Fire Department spokesman Capt. Jim Doucette said.

As the boys were walking home to change clothes, the 12-year-old boy lit his friend on fire, Doucette said.

The 13-year-old was trying to extinguish the flames on him when his friend lit him on fire a second time, Doucette said.

It's not clear if the 12-year-old intended to hurt his friend or was being playful, Doucette said.

Leong said the 12-year-old was arrested for arson and taken to the Sacramento County Juvenile hall.

Doucette said the motive may have simply been curiosity. "We don't know that he tried to hurt him, but he purposely lit him on fire to see what would happen — twice," Doucette said.