Prime Minister David Cameron and US president Barack Obama have discussed the worsening situation in Gaza during a phone conversation, Downing Street said.
A No 10 spokeswoman said: "Both leaders reiterated their support for Israel's right to take proportionate action to defend itself from the barrage of rocket attacks from Gaza."
The two leaders also discussed Iran's nuclear programme and "agreed that we should keep up our efforts to negotiate a lasting agreement which gives the world confidence that the nuclear activities of Iran are exclusively for peaceful purposes".
Yesterday a group of pro-Palestinian demonstrators had to be ejected from the Cabinet Office after staging a protest against Israeli military action in Gaza..
The loose-knit group, who call themselves London Palestine Action, posted photos on their Facebook page of demonstrators linking arms as they sat in the lobby of the Whitehall building at around 4.30pm.
Police officers were called to remove the small group, who were chanting anti-Israel slogans and carrying banners reading "Stop arming Israel".
Leila White, an art history student at King's College, took part with up to 25 fellow activists in the 45-minute protest, in response to the Israeli ground offensive which began in Gaza on Thursday.
The group locked themselves to railings before unfurling banners and chanting, demanding to speak with Deputy Prime Minister Nick Clegg or a Cabinet Office official.
Ms White said: "By allowing arms exports to Israel to flourish, the UK Government is providing material and political support for Israel's violent oppression and collective punishment of Palestinians, including the current massacre in Gaza."
She added: "There has not been enough condemnation of Israel's military action. Basically, we want the UK Government to invoke an arms embargo against Israel."
The Metropolitan Police said no one was arrested before the group moved on.
The group, who have previously staged flashmob demonstrations in the capital, describe themselves as "a network of people in London taking creative action against Israeli apartheid through BDS (boycott, divestment and sanctions) and other effective, participatory Palestine solidarity work".
A national march and rally by the Palestinian Solidarity Campaign (PSC) will take place in central London today.
The march will form up in Whitehall from midday before making its way through the city to a static rally outside the Israeli embassy near Kensington High Street.
Labour leader Ed Miliband, who visited Israel earlier this year, said the "horrifying deaths of hundreds of Palestinians" could not be justified or defended.
He said: "I have seen for myself the fear in Israel from the unjustified and appalling rocket attacks from Hamas in Gaza.
"I defend Israel's right to defend itself against rocket attacks.
"But I cannot explain, justify or defend the horrifying deaths of hundreds of Palestinians, including children and innocent civilians.
"And as a party we oppose the further escalation of violence we have seen with Israel's invasion of Gaza.
"Because we have been here before and we know what happens next: m ore loss of life, more Palestinian suffering, more hatred and more recruits to the ranks of terrorist groups like Hamas.
"This escalation will serve no lasting purpose and win Israel no friends.
"There can be no military solution to this conflict. The only solution is two states living alongside each other in peace and security.
"So the violence must stop a nd a political way forward must be found."