An anti-war march and rally is to be held in London as part of protests across the world to demand that US and UK troops pull out of Iraq.
Last year's protest included a mass "die-in"
The Stop The War Coalition say they hope "several tens of thousands" of people will demonstrate on 18 March.
The event marks the third anniversary of the start of the Iraq conflict.
Similar demonstrations are due to be held in cities in Iraq, as well as in America, Japan, Mexico and other parts of Europe.
Protesters in London will demand the immediate withdrawal of British troops from Iraq.
And they will urge America not to attack Iran. So far, US officials have only urged support for internal opposition to the Iranian Government, which it suspects of harbouring nuclear arms ambitions.
The Stop The War Coalition says the spread of protests underlines the extent of opposition to the continuing presence of US-led alliance troops in Iraq.
Convenor Lindsey German said: "Tony Blair tells us that we are there to protect the Iraqi people and help them build democracy.
"In reality all opinion polls show that the Iraqi people want the troops to leave. With thousands of Iraqis set to take to the streets demanding troops out his lies will be well and truly exposed."
Police said at least 750,000 people marched against the war in 2003. The organisers put the figure at closer to two million.
Ms German said families of British soldiers killed or injured in Iraq were expected to join this year's protest, as were many British Muslims.
Labour MP Jeremy Corbyn said the Iraq war had been "disastrous" and he predicted huge support for the protest.
"We need an exit strategy now before more lives are lost," he said.
Defence Secretary John Reid on Monday said the public should be more understanding of the "unprecedented challenges" faced by British troops in foreign battle zones, especially Iraq.
He has said conditions in Iraq are "well on the way" to being suitable for a withdrawal of UK troops.
But before they leave, the threat of insurgents must be manageable, with Iraqi forces more able to handle the problem, he says.
He also wants to ensure local government bodies are effective and that the UK can be confident it can provide support to local forces if necessary.