Thousands of protestors marched from the White House to Congress yesterday waving placards demanding an end to the war in Iraq, the return of US troops, and the impeachment of President George W Bush.
Organisers said 197 people, including dozens of veterans and activists, were arrested as they crossed police lines.
Police put the number of arrests at 189.
The group that organised the march, the Act Now to Stop War & End Racism (ANSWER) coalition, said authorities also used pepper spray to disperse the crowd.
Mr Bush announced in a speech on Thursday that the size of the US force in Iraq would decrease by about 21,500 combat troops by mid-2008, with the first 5,700 soldiers leaving Iraq in December.
Currently 169,000 US troops are in Iraq, up from 130,000 before Mr Bush announced a 'surge' of US forces in January.
Iraqi suicide attack
At least five people have been killed in a suicide attack in northern Iraq.
Ten more were wounded when a suicide bomber triggered his explosive vest in a crowded cafe in a town near Kirkuk.
The attack occurred in the town of Tuz, 70km south of Kirkuk.
At least 34 people have been killed in bomb and gun attacks in Iraq since the start of the Muslim holy month of Ramadan on Thursday.
The Islamic State of Iraq, which is affiliated to al-Qaeda, vowed a new offensive during Ramadan.
It also warned it would target Sunni leaders who support US troops in Iraq, and claimed the assassination on Friday of Sunni sheikh Abdul Sattar Abu Reesha who had led the fight against al-Qaeda alongside US forces in Anbar province.
US forces in Iraq claim they have captured one suspected al-Qaeda fighter linked to the killing.
The suspect was detained during an operation yesterday at Balad, 70km north of Baghdad.