A mother who checked her son's social media usage discovered a plot to shoot him outside his school.

The woman was looking at his Facebook page when she spotted "specific threats" by two teenagers, who said they were going to go to his high school and gun him down.

She alerted West High School in Salt Lake City, Utah, and police found the pair sitting in a car near the school.

Officers found a loaded gun in the vehicle, along with marijuana and a large amount of cash.

Detective Greg Wilking told a local television channel "They were threatening his life of Facebook - pretty credible threats".

"When they're posting it on social media and then they're actually where they said they were going to be and they have a weapon, I would say that's a pretty credible threat".

Police also say there were photographs posted on Instagram by the pair "involving a weapon".

Detectives say they are looking at whether the dispute was gang-related, and linked to a drive-by shooting last week.

The two suspects, aged 16 and 17, cannot be named due to their ages.