LONDON (AFP) -- Activists, claiming a groundswell of anti-war sentiment not seen since the U.S.-led invasion of Iraq, were preparing to stage a mass protest here against the conflict in Lebanon and demand a ceasefire.

The rally organized by the Stop the War Coalition is to start Saturday at 12 noon at London's Hyde Park, pass the U.S. embassy and British Prime Minister Tony Blair's office before ending up at the Houses of Parliament. "Leave children's shoes on Tony Blair's doorstep," the coalition urged protestors on its website ahead of the demonstration. "Almost half of those killed so far in Lebanon are children."

Shoes should be left at The Cenotaph memorial on the street outside his office "to express our horror at his complicity in war crimes, which have lead to the slaughter of so many children in Lebanon, Gaza, Iraq and Afghanistan," it said.

In a press statement earlier in the week, it said: "We need the biggest possible turnout on Saturday's emergency demonstration.

Resisting international calls for an immediate ceasefire Blair has sided with the U.S. and Israeli governments in demanding that Israel's political and security concerns be answered before a ceasefire is agreed. The coalition said the demonstration can "intensify" the anti-war pressure from within Blair's governing Labor Party, his cabinet and people nationwide to "breaking point."

"Stop the War has not experienced anything like it since the run up to the Iraq war in 2003. Over 1,000 people every day are contacting the Stop the War office," it said.

The Independent newspaper said as many as 100,000 people are predicted to take to the streets around Parliament Square.

A letter bearing 40,000 signatures will also be handed in at Blair's Downing Street office, calling on the premier to work towards ending the "bloodshed and destruction unfolding daily," the newspaper said.

Other organizers of the protest include the British Muslim Initiative, CND, the Palestine Solidarity Campaign and Lebanese community associations.