WASHINGTON (AP) — Police are responding to an incident near the U.S. Capitol grounds, and a witness says shots were fired.

A car was stopped at a checkpoint Wednesday morning, according to the witness, and police ordered a woman driving a vehicle to stop.

Several gunshots were heard. An ambulance is on the scene.

Police have yet to issue additional details.

The witness, on Capitol Hill to visit lawmakers, declined to permit her name to be used.