Coordinated global protests, from Seoul to Spain and San Francisco, also called for an end to the US-led occupation and Israel's hold on Palestinian territory, but were small and only a faint shadow of huge pre-war peace rallies.

In the first major protest in Britain since the war ended in April, demonstrators -- some 20,000, by police estimates -- vented their anger at the invasion and the reasons given for it.

The march added to pressure on Prime Minister Tony Blair, whose popularity and trust ratings have sunk in the aftermath of the Iraq conflict, in which Britain was America's staunchest ally.

The failure to unearth any weapons of mass destruction -- the main justification for war -- and the public inquiry into the suicide of a government expert on Iraq have plunged Blair into the worst political crisis of his six-year tenure.