OKLAHOMA CITY - An Oklahoma City high school downgraded a "lockdown" to a "lockout" Friday morning, as police continue to investigate reports of a suspicious vehicle. 

U.S. Grant High School, located at 5016 S. Penn. in Oklahoma City, is on lockout, meaning classes are resuming as normal inside the school, but no one is being allowed to enter the building unless they are on the pick-up list and show identification of their child.

School officials said they were made aware of a group of people in a car outside the school. A witness reported seeing a gun inside that car. Police said the principal went outside and approached the car, but it took off. 

The school was placed under a brief lockdown. Officers searched the area but they couldn't find the vehicle. The lockdown was then downgraded to a "lockout." Classes will resume. 

One officer will remain at the school. School officials said they will lift the lockout when police give them the "all clear."

School officials said parents have been notified of the situation, and are asked to call the school (405)-587-2200 if they have questions or concerns.