Police arrested 18 protesters in San Francisco marking the first anniversary of the US invasion of Iraq.
Several hundred demonstrators marched down San Francisco's main Market Street and others gathered in front of the worldwide headquarters of Bechtel, the privately held engineering firm involved in Iraq reconstruction projects.
A few people chained themselves together with plastic piping. Others played drums and sang.
A police spokeswoman said those arrested were charged with blocking the street and refusing to move when requested.
Liberal San Francisco has been a leading US centre of opposition to President George W. Bush's decision to wage war against Iraq, and thousands were arrested a year ago in large demonstrations after the start of the conflict.