A schoolgirl hostage was fatally wounded before a gunman killed himself as armed police stormed a high school in the western state of Colorado, police has said.
Park County Sheriff Fred Wegener said the unidentified gunman turned his weapon upon himself yesterday after shooting one of two girls being held hostage at Platte Canyon High School in Bailey, 56 kilometres south of Denver.
The man, believed to be in his 30s, opened fire as police entered a second floor classroom after the gunman -- who claimed to be carrying a bomb -- broke off contact with hostage negotiators.
"Entry was made, the suspect shot one of the hostages and then shot himself, that's what it looks like at this time," Wegener told reporters.
The second hostage escaped unharmed.
The critically injured girl was airlifted to St Anthony Central Hospital in Denver but died later on Wednesday.
"I don't know the identity of the gunman, I don't know why he wanted to do this and hopefully the investigation will reveal who it is," he told reporters.
The siege began when the gunman entered the school at around 12:00 pm and fired "more than one shot", claiming to be carrying a bomb in a rucksack, police said.
The gunman had initially taken six hostages but released four of them during the afternoon.