WASHINGTON — Police arrested more than a dozen people Wednesday morning who crossed a barricade and blocked entrances at the Internal Revenue Service building, the start of a day of protests marking the fifth anniversary of the U.S. invasion of Iraq.

A crowd gathered outside the IRS headquarters, chanting "This is a Crime Scene" and "You're Arresting the Wrong People." A marching band led protesters down the street near the National Mall and around the IRS building before dozens demonstrators gathered at the entrance.

Protesters blocked the main entrance for a time, but no federal workers appeared to be trying to use those doors. Police detained 13 people who sat down at a side entrance.

The demonstrators said they were focusing on the IRS because it gathers taxes that are used to fund the war.

Anti-war protests and vigils were planned throughout the day around the nation.

At the American Petroleum Institute in downtown Washington, dozens of protesters held signs reading "Out of Iraq" and "No war, no warming," and chanted "No blood for Oil!"

Craig Etchison, 62, a retired college professor from Cumberland, Md., and a Vietnam veteran, said he has been protesting the war for years.

"I've watched with horror as Bush has lied about this war," he said in front of the building. "I'm appalled at the number of civilians we've killed just as we did in Vietnam."

College students from New Jersey to North Dakota have planned walkouts, while students at the University of Minnesota vowed to shut down military recruiting offices on campus.

"This is the first time coordinated direct actions of civil disobedience are happening," said Barbra Bearden, communications manager for the group Peace Action. "People who have never done this kind of action are stepping up and deciding now is the time to do it."

In suburban Miami, Linda Belgrave, a sociology professor at the University of Miami, and a handful of protesters dressed in black waved anti-war signs at drivers stuck in early morning rush-hour traffic near the U.S. Southern Command complex. Belgrave said the group planned to lay flowers at the complex's entry fence later Wednesday morning.

"This is the beginning of the sixth year of this horror and it's got to end," said Belgrave, 57.

The Iraq war has been unpopular both abroad and in the United States, although an Associated Press-Ipsos poll in December showed that growing numbers think the U.S. is making progress and will eventually be able to claim some success in Iraq.

The findings, a rarity in the relentlessly unpopular war, came amid diminishing U.S. and Iraqi casualties and the start of modest troop withdrawals. Still, majorities remain upset about the conflict and convinced the invasion was a mistake, and the issue still splits the country deeply along party lines.

Activists cite frustration that the war has dragged on for so long and hope the more dramatic actions will galvanize others to protest.

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Associated Press writers Karen Mahabir in Washington, John Christoffersen in New Haven, Conn., and Jennifer Kay in Miami contributed to this report.