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

Smithsonian spokesman John Gibbons said a large group of demonstrators, estimated at 100 to 200 people, arrived at about 3 p.m. and tried to enter the National Mall museum. When a security guard stopped group members from entering, saying they could not bring in signs, he was apparently held by demonstrators, Gibbons said. A second guard who arrived used pepper spray on at least one person and the crowd dispersed, he added.

A number of groups have been demonstrating in the city in the past week. The group that arrived at the museum Saturday included individuals taking part in the October 2011 Stop the Machine demonstration in the city’s Freedom Plaza, which has an anti-war and anti-corporate greed message. The group also included protesters affiliated with Occupy D.C., a group modeled on 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, Va., said he was among dozens of people sickened by the pepper spray. He said he got sick even though he was outside the building when the spraying began.

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

Swanson, who says he has been part of the Freedom Plaza protest, says protesters were not looking to shut down the museum but to make a point about the massive military spending and the use of deadly drones. He said the security officers got aggressive after some protesters unfurled a protest banner inside.

He posted videos on his blog, warisacrime.org, that shows a security officer yelling "Get back" as pepper spray is apparently used. Several people fell to the ground outside in agony as others coughed, rubbed their eyes and fled the building.

Pete 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.

Ann Wilcox, a lawyer working with Stop the Machine, said a 19-year-old woman from Madison, Wis., was arrested by police. She paid a fine and was released later Saturday. Wilcox said the protesters went to the Air and Space museum to demonstrate against a drone exhibit.

The museum has an exhibit, "Military Unmanned Aerial Vehicles," that covers the history of unmanned aircraft and their current use as offensive weapons. Drones are often called the weapon of choice of the Obama administration, which quadrupled drone strikes against al-Qaida targets in Pakistan’s lawless tribal areas, up from less than 50 under the Bush administration to more than 220 in the past three years.

The museum is expected to re-open Sunday.