A series of demonstrations are to take place across the UK to try and stop the Israeli air strikes on Gaza.
The protests are due to be held at 18 locations including Portsmouth, Manchester, Hull, London and Glasgow.
They come after several days of smaller demonstrations around the country, including outside the Israeli Embassy in Kensington, west London.
Israel’s government has said it is defending its citizens from Palestinian rocket attacks.
The government launched the offensive after Palestinian rockets were fired into Israel’s southern regions, breaking a six-month truce.
But Lyndsey German, of the Stop the War Coalition, said Israel’s actions were not “a defence measure”.
She said there would be “tens of thousands” of people in London alone and this “is just the start of the campaign”.
“If there is an invasion of Gaza, as looks likely, by the Israeli army, if the blockade continues with people suffering from shortages of food and medicine, then I think this will grow.
“This is Israel being aggressive, this is Israel attacking one and a half million people who already live in great poverty, in great difficulty.”
More than 30 organisations, including the British Muslim Initiative and the Stop the War Coalition, have worked together to organise the series of protests.
Former model Bianca Jagger and singer Annie Lennox have supported the action, and have also called on American president-elect Barack Obama to speak up against the bombardment.
Ms Lennox told the BBC that both sides were “wrong” and a total ceasefire was the only sensible solution.
She said the intervention of President George W Bush, who has described Hamas’s rocket attacks as an “act of terror”, was not helping the situation.
She said: “The problem is, from my perspective, they are pouring petrol onto the fire.
“They have to sit down. This is a small window of opportunity just before things kick off.
“For every one person killed in Gaza, they are creating 100 suicide bombers. It’s not just about Gaza, it’s about all of us.