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WASHINGTON (CNN) -- Two Presbyterian ministers were among 71 people arrested during a series of peaceful protests against the Iraq war Tuesday, said a spokeswoman for a group participating in the protests.

Demonstrators held sit-ins, prayer services and sing-alongs at four locations in the Capitol complex, including the central atrium of the Senate Hart Office Building.

The demonstrations were reminiscent of the Vietnam era, with protesters strumming guitars, singing peace songs, holding flowers and wearing hats made of balloons. (Watch war protesters face the music -- 1:28)

Senate staffers watched the demonstrators from their offices. Protesters said that several workers gave them a thumbs-up or other signs of approval. (Watch how the protests are part of a highly charged day in Washington -- 2:23 )

"We are trying to protest a lack of civil liberties and to try and end a war culture," said protester Alex Bryan of New York.

Thirty-three of those arrested were charged with unlawful conduct inside the Hart Building, said Sgt. Kimberly Schneider of the Capitol Police.

Thirty-eight more demonstrators were arrested at separate protests near the Capitol, she said. Of those, 23 were charged with crossing a police line and 15 were charged with demonstrating without a permit.

All of those arrested were cooperative with police, Schneider said.

The National Campaign for Nonviolent Resistance, which has organized dozens of anti-war protests around the country, coordinated Tuesday's effort, which included several religious and secular groups.

Among those arrested during the demonstrations were two Presbyterian ministers, a Catholic activist and a member of a Quaker group, said Jennifer Kuiper, spokeswoman for The Declaration of Peace, one of the groups participating in the protests.

Both groups apparently expected participants to be arrested. On a notice posted at The Declaration of Peace Web site, the protests are described as an "interfaith religious procession around the Capitol, followed by peace presence and nonviolent resistance, including risking arrest at the U.S. Senate."

The National Campaign for Nonviolent Resistance Web site adds, "Those willing to engage in nonviolent acts of civil resistance against the war and occupation are encouraged to join us. We also enthusiastically call upon those who cannot risk arrest, but who are willing to support those who do."

Despite a rising tide of war opposition, the protesters said they represent no party or political movement.

Baptist minister Jamie Washam of Wisconsin, who led an interfaith service during the protests, said she is adamantly opposed to the war.

"My congregation wants peace," she said. "And I think it's an offense to God."

Tuesday's events in Washington were part of 375 protests and other activities being held around the country this week in opposition to the war, according to The Declaration of Peace.

There were hundreds of arrests in a protest organized by the National Campaign for Nonviolent Resistance a year ago. On September 26, 2005, 371 people were arrested during the "Resist and Remember" protest in Washington, one of the organization's founders, Gordon Clark, wrote in an online article.

Of those, 104 were arrested at the White House for refusing to leave after being denied an audience with President Bush, Clark wrote.