Protests have been taking place across the world to mark the first anniversary of the start of the Iraq conflict.
Hungarian protesters formed a human peace sign in Budapest
In New York, thousands marched through central Manhattan and similar rallies were held in other major US cities.
In Europe, one of the biggest protests was in Rome, where up to 300,000 marchers jammed the streets.
And in London, where two protesters climbed the Big Ben clock tower near the Houses of Parliament, police said around 25,000 joined demonstrations.
The Big Ben stunt sparked concerns about security around the capital's landmarks, which is supposed to be at a high level to guard against a possible terrorist attack.
In New York City and Chicago - where two of the biggest rallies took place - security was tight, with dozens of police officers overseeing protesters.
"I support the troops, I just don't support the war," said one woman protester, whose son was killed in the recent conflict.
"They are sitting ducks."
Hollywood star Woody Harrelson was among tens of thousands who took to the streets in the western US cities of San Francisco - for a second day - and Los Angeles.
Latin American countries such as Chile, Venezuela and Brazil also held protests.
In Rome, riot police stood by as a festive and trouble-free procession wound its way through the ancient streets.
Protesters in London scaled the landmark clock tower, Big Ben
A truck pulled a caricature of Italian Prime Minister Silvio Berlusconi as the lap dog of US President George W Bush.
In the Hungarian capital, Budapest, demonstrators holding blazing torches formed a human peace sign in the city's Heroes' Square and called for Hungarian troops to be withdrawn from Iraq.
The Spanish city of Madrid, still reeling from the 11 March bomb attacks, saw around 100,000 protesters marching through the city, waving banners and chanting "No to the war".
In Barcelona, organisers said up to 200,000 marchers took part in a protest, many carrying an enormous "Peace" sign.
The day of worldwide rallies began in Australia and New Zealand, with protests held across Asia.
Thousands of Australians took to the streets calling for the withdrawal of the 2,000 Australian troops serving in Iraq, who were deployed despite huge public opposition.
In Sydney, protesters carried a 1.5 metre (five foot)-high effigy of Prime Minister John Howard in a cage to represent Australian suspects detained at the US military prison camp in Guantanamo Bay.
In Tokyo, protest organisers said 30,000 people joined a march to voice opposition to Japan's involvement with the Iraqi occupation - Japan has sent 1,000 personnel to Iraq, its largest foreign deployment since World War II.
There were also protests in Thailand, the Philippines and Hong Kong.
Hundreds of demonstrators took to the streets of Middle Eastern capitals to denounce the war, although in Iraq itself there were no public demonstrations for or against the war.
Correspondents say the majority of Iraqis are pleased that former President Saddam Hussein has been ousted, but resent the occupation of their country and are impatient to have their own government.
Speaking on the eve of the anniversary, President Bush said differences over the Iraq war belonged to the past.
"Any sign of weakness or retreat simply validates terrorist violence and invites more violence for all nations," he said.