Tens of thousands of people have taken part in a rally for Gaza in London.
The demonstration came amid renewed violence between Israel and Palestinian militants after a three-day ceasefire ended on Friday.
An emergency appeal in the UK for people affected by the conflict in Gaza has raised £4.5m in less than 24 hours, the Disasters Emergency Committee said.
Meanwhile, David Cameron and Barack Obama have expressed "serious concern" about the renewed hostilities.
The UK prime minister and US president, who discussed the ongoing fighting during a phone call, have both called for another ceasefire. They condemned Hamas for launching rockets from civilian areas and said Israel needed to show "restraint".
The Department for International Development (DfID) is sending a team of NHS medical experts to the region to help those injured in Gaza.'Noisy but peaceful'
Saturday's demonstration, organised by the Stop the War coalition and the Palestine Solidarity Campaign, saw participants march past the US embassy on their way to a rally in Hyde Park.
Speakers there included Labour MP Diane Abbott, who told the crowd British people "stand in solidarity with the people of Gaza". She said it was the "biggest demonstration yet" about Gaza.
The BBC's Mark Sanders, at the rally, described it as "a very noisy protest but a peaceful one".
Protester Philip McCowen, 59, from Bristol, said: "The massacre of children is outrageous. The bombing of hospitals is outrageous. Collective punishment is a crime against humanity."
Yiftah Curiel, a spokesman for the Israeli embassy in London, told the BBC: "We don't have a problem with the protest per se; we have a problem with people expressing support for a terror organisation which is designated in the UK [Hamas] and which today is the key obstacle to the prosperity of Gaza."
More than 1,900 Palestinians, mostly civilians, have been killed in four weeks of Israeli attacks in the Gaza Strip, the UN says.
Sixty-seven people have died on the Israeli side, three of them civilians.
Israel says it is acting to protect its citizens from rockets fired from Gaza. Hamas, which controls Gaza, has demanded that Israel end its blockade of the territory.