Thousands of demonstrators have been holding anti-war rallies as the anniversary of the US-led invasion of Iraq nears.
Washington's protesters braved freezing temperatures
In Washington, thousands braved cold temperatures to march to the Pentagon carrying placards denouncing the war.
Tuesday marks four years since the war began. Tens of thousands of Iraqis have died as well as some 3,200 US troops.
Protests took place in other US cities including Los Angeles, in European capitals and in Australia.
'Shadow of death'
US anti-war activist Cindy Sheehan, whose soldier son died in Iraq, said those marching were walking "in the shadow of the war machine".
Spain's march was among the world's largest
"It's like being in the shadow of the death star. They take their death and destruction and they export it around the world. We need to shut it down," she said.
Many carried black and yellow signs urging the US to leave Iraq as they made their way across the Potomac River from the Lincoln Memorial.
Organisers said freezing temperatures had probably discouraged some from taking part in the march which followed the same path as a key rally against the Vietnam War in 1967.
Speakers called variously for the withdrawal of US troops, the impeachment of President George W Bush and the closing down of the Pentagon.
Several thousand other people, many of them members of the armed services, gathered in counter rallies in support of the war, playing the Battle Hymn of the Republic.
In Los Angeles, police estimated that up to 6,000 people demonstrated in anti-war rallies which included flag-draped coffins being carried through the streets of Hollywood.
Spain's protests were the largest in Europe, with some estimates putting the number of people taking part at 100,000.
In the capital, Madrid, protesters waved placards denouncing President Bush and former Spanish Prime Minister Jose Maria Aznar for "war crimes".
Film director Pedro Almodovar was among those who took part.
He said he was present to protest against "the barbarities they have been committing in Iraq for the past four years".
In the Turkish city of Istanbul, more than 3,000 took part in protests, carrying signs reading "Bush go home" and "We are all Iraqis".
Hundreds also gathered to voice their opposition to the Iraq war in the Spanish cities of Seville, Cadiz and Granada as well as the European capital cities of Athens, Copenhagen and Rome.
In Australia, small demonstrations were held in both Sydney and Melbourne.