Thousands of pro-Israel supporters have gathered in London's Trafalgar Square to call for an end to the violence in the Middle East.
Organisers said they wanted people in Gaza and Israel to live in peace, but argued that Hamas must accept responsibility for the conflict.
Demonstrators told the BBC they felt the rocket hits and losses Israel had suffered had been downplayed.
Chief Rabbi Dr Sir Jonathan Sacks said he wanted Hamas to "say yes to peace".
About 850 Gazans and 13 Israelis have reportedly died in 16 days of fighting.
They said the number of Israeli deaths should not be considered disproportionate to the number of Palestinian deaths, because Israelis were lucky and escaped their houses before they were hit by Palestinian rockets.
Thousands of young British Jews attended the rally
The BBC's Raffi Berg, who was at the rally, said there was a festival atmosphere as people cheered and applauded a succession of speakers who called for peace for Israel and the Palestinians.
However, an address by Rabbi Sacks was briefly interrupted when a protester, yelling through a loud-hailer, jumped into a fountain and scuffled with security officials in the icy water before being dragged out.
Police said they estimated 4,000 people are at the event in central London. Organisers say 15,000 people have turned up.
It was the first major rally organised by the Jewish community in the UK over Israel's offensive against Palestinian militants in Gaza.
It comes after prominent British Jews wrote an open letter calling on Israel to halt operations in Gaza.
We look upon the increasing loss of life on both sides of the Gaza conflict with horror
Letter by prominent British Jews
Rabbi Sacks told the crowd: "All it took to avoid this suffering was for Hamas to stop firing rockets on Israeli citizens.
"Let a voice go out today from here in Trafalgar Square, and other gatherings being held, that we want peace."
"We say to those who criticise Israel: You want Palestinian children to grow up with hope, so do we.
"You want Palestinians to be able to live with dignity, so do we."
He said the day would come when Israelis and Palestinians would live together in peace.
"It could be hundred years away, or it could be today, it is up to Hamas and the people that give them arms, for the sake of Israeli children and the Palestinian children, we say, let it be today."
Henry Grunwald, president of the Board of Deputies of British Jews, addressed the crowd saying: "We are here because we believe in peace, because we believe in life, and because we want peace in life.
"The events of the past two weeks have not been a war on the people of Gaza but war on the people using them as human shields."
A small group of pro-Palestinian protesters - estimated by police to number between 80 and 100 - were being kept separate from the main body of the rally by mounted police.
Another pro-Israel peace rally is also being held in Manchester.
Meanwhile the letter, published in the Observer, warns the military action, far from improving security, will strengthen extremism and destabilise the region.
Prominent rabbis, academics and political figures supported the open letter.
Some pro-Palestinian protesters attended the mainly peaceful rally
They write: "We look upon the increasing loss of life on both sides of the Gaza conflict with horror.
"We have no doubt that rocket attacks into southern Israel, by Hamas and other militant Palestinian groups, are war crimes against Israel.
"No sovereign state should, or would, tolerate continued attacks and the deliberate targeting of civilians.
"Israel had a right to respond however, we believe that now only negotiations can secure long-term security for Israel and the region."
On Saturday thousands of pro-Palestinian demonstrators marched through London to call for an immediate ceasefire in Gaza.
The protest started peacefully but there were confrontations as police tried to move demonstrators away from the gates of the Israeli embassy.
Protests also took place in Edinburgh, Aberdeen, Belfast, Newcastle and Southampton.
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