Galvanised by the Anglo-American attack on Iraq, thousands of anti-war activists around the world have taken to the streets, with more than 1,000 people arrested while demonstrating in San Francisco.
In the US the anti-war groundswell also brought out thousands of counter-demonstrators. One in Mississippi carried a sign saying, "Support the US or keep your mouth shut."
"This is no ordinary day," said Jason Mark, a San Francisco activist. "America is different today: We've just launched an unprovoked, unjust war."
Protests erupted in Asia and Australia. The streets of Melbourne were choked with 5,000 protesters demanding an end to the conflict as mock air raid sirens wailed.
In Islamabad, Pakistan's religious right urged anti-war activists to stage marches, but withdrew a call for a nation-wide strike saying it would hurt ordinary Pakistanis trying to make a living.
In Bangkok, about 100 Thai anti-war activists marched on the US Embassy.
Indonesia, the world's largest Muslim nation, girded for large protests and police beefed up security at foreign embassies and businesses.
Hundreds of thousands of protesters marched on American embassies in European capitals and in Manila, the Philippines.
In Egypt, riot police used water cannons and attack dogs to keep anti-war demonstrators away from the US Embassy. Protesters hurled stones, pounded cars and shouted against the United States and Egypt's leaders.
Police reports said 37 protesters and police were injured.
In Buenos Aires, Argentina, police fired tear gas grenades and rubber bullets to scatter demonstrators who stoned the US Embassy.
Italians marched by the thousands in Rome and other cities, and the country's powerful trade unions organised two hour work strikes.
In Athens, more than 100,000 people marched to the US embassy, where their rally ended peacefully. But violence broke out in the northern Greek city of Thessaloniki, where demonstrators set fire to a car and hurled eggs and red paint at police.
In the United States, San Francisco saw some of the heaviest anti-war activity.
Thousands in roving bands temporarily took control of some city centre streets. Smaller splinter groups broke windows, heaved debris into streets and occasionally scuffled with police.
Police wearing helmets and carrying night-sticks made at least 1,025 arrests.
Hundreds of protesters marched in Pittsburgh and 50 arrests were made.
Anti-war protesters blocked traffic in Washington. Dozens of activists temporarily shut down inbound lanes of a Potomac River crossing, holding up the morning traffic.
Outside the White House, about 50 stood in chilly rain and shouted, "No blood for oil!" About 300 protesters rallied in the evening.
In New York, anti-war protesters converged in a steady rain on Times Square at rush hour.
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