In an emotional speech, Annie Lennox said there had to be a different way forward.
"A few days after Christmas I came downstairs, put the television on and saw smoke pyres emanating from buildings and it shook me to the core," she said.
"I was thinking, as a mother and as a human being, how was this going to be a solution to peace?
"It's a question of human rights, human values that goes beyond Jewish, Muslim, nothing to do with any of that. There has to be a place ultimately where people come to the table."
In a strongly-worded condemnation of Israeli bombing, Jewish comedian Alexei Sayle said Israel has an idea it was being noble but was using the "psychology of the murderer" to explain the attacks.
Former Mayor of London Ken Livingstone called for the European Union and the UK to withdraw their ambassadors from Israel to signal disapproval with the "slaughter and systematic murder of innocent Arabs".
Appeal to Obama
Respect MP George Galloway suggested Israel's attacks would create a new generation of radicals around the world.
"We will be very, very lucky if the explosions taking place in Gaza today don't blow up in our own face at some time in the future," he said.
Meanwhile, activist Bianca Jagger condemned the attack by Hamas against innocent Israeli citizens, but called for the international community to guarantee the immediate halt of the "disproportionate, unlawful use of force by Israel".
She added: "I would like to make an appeal to President-elect Obama to speak up.
"People throughout the world were hopeful when he was elected and we must appeal to him to ask for the immediate cessation of the bombardment of the civilian population in the Gaza Strip."
Earlier, more than 100 protesters gathered outside Egypt's London embassy demanding the country fully open its border with Gaza to allow humanitarian aid in and let the sick and injured out so they could go to hospital.
General Secretary of the Palestine Solidarity Campaign Betty Hunter said: "Egypt has to stop colluding with Israel and do this now."
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