A gunman killed two staff at a private school owned by a prominent Saudi billionaire in Riyadh on Wednesday, a security source told AFP.
The school was closed and no children were there at the time, said the US embassy in Riyadh.
Police were hunting a suspect of Iraqi origin who worked at the school, the security source said, after the rare shooting.
"A teacher took a gun and then he went to the school room and he killed the assistant school principal and one of the employees," said the source who asked not to be identified because a formal statement would come later from Riyadh police.
Investigators are treating the case as a criminal matter and "not a terrorist incident," the source said.
Saudi media spoke of "disagreements" between the suspect and victims.
"There has been a shooting at Kingdom School in Riyadh," the US mission said on its Twitter account.
"School (is) closed, no children present. Please avoid area," the Twitter post said, without elaborating on casualties or motives behind the shooting.
By late afternoon an AFP photographer observed only one police car entering the school grounds, which were quiet, and nobody answered the school's main phone line.
Most schools in Saudi Arabia are on holiday.
Kingdom School is part of a group owned by Prince Alwaleed bin Talal, chairman of Kingdom Holding Co whose diversified investments include Citigroup and Time Warner.
The school, located in central Riyadh, opened in 2000 and offers boys' and girls' education from kindergarten to high school, according to its website.
The school has both a Saudi curriculum and an international programme leading to an American diploma.
Kingdom Holding says on its website that the schools group has more than 4,000 students and 300 teachers at various locations in Riyadh.