The National Air and Space Museum in Washington, D.C., was closed Saturday after anti-war demonstrators descended on the building to protest a drone exhibit and security guards used pepper spray to repel them, sickening a number of protesters.

A group of roughly 100 to 200 people arrived around 3 p.m. and tried to enter the National Mall museum when security guards stopped the protesters from entering, saying they could not bring in their signs, Smithsonian spokesman John Gibbons said.

At least one person was pepper-sprayed when the crowd pinned a guard against a wall and another guard came to his rescue, Smithsonian spokesperson Linda St. Thomas said. Apparently, the demonstrators held the guard. A second guard arrived and used pepper spray on at least one person and the crowd dispersed.

The group also included protesters affiliated with Occupy D.C., an offshoot of the Occupy Wall Street protests in New York City; Occupy D.C. has been holding marches and meetings in Washington's McPherson Square.

David Swanson, 41, of Charlottesville, Virginia, said he was among dozens of people sickened by the pepper spray.

"I began choking and vomiting and got a headache," he said.

Swanson, who said he has been part of the Freedom Plaza protest, maintains that the protesters were not looking to shut down the museum, but rather were trying to make a point about huge military spending and the continued use of deadly drones.

After protesters unfurled a protest banner, Swanson said some of the security officers got aggressive. Videos depicting a security officer yelling "Get back" as pepper spray was used, were posted to Swanson's blog, warisacrime.org.

Peter Piringer, a D.C. fire department spokesman, told The Associated Press on Saturday evening that medics treated or evaluated a dozen people at the scene, but that no one was seriously hurt by the pepper spray.

Legba Carrefour, who is working with Occupy D.C., said a number of individuals joined the march to the museum following an afternoon meeting of the group.

The museum currently has an exhibit, "Military Unmanned Aerial Vehicles," that covers the history of unmanned aircraft and their current use.

The museum was expected to re-open today.