Police shot an armed man at an entrance of the U.S. Capitol visitor center Monday, March 28 sparking panic during the busy spring tourist season in a city on heightened alert following terror attacks in Brussels, AFP reports.

The suspect, who police said was known to authorities, was hauled into custody and transported to hospital, where he underwent surgery. The incident was not believed to be terror-related.

A female bystander suffered what police said appeared to be minor injuries and was hospitalized.

The incident prompted an hour-long lockdown on Capitol Hill in the heart of Washington, where staffers and frightened visitors were ordered to shelter in place.

"We believe that this is an act of a single person who has frequented the Capitol grounds before and there is no reason to believe that this is anything more than a criminal act," Capitol police chief Matthew Verderosa told reporters, according to AFP.

Verderosa said the suspect, who he did not identify, had entered a security checkpoint at the visitors center.

Local media identified the suspect as Larry Dawson of the southern state of Tennessee. Richard Burr, a North Carolina senator, told CNN the suspect was "mentally disturbed."