In a statement issued by the Foreign Office in London, Mr Miliband renewed Britain's calls for an urgent ceasefire in Gaza and the immediate halting of violence on both sides.
As Israel masses troops on its border with Gaza, Prime Minister Gordon Brown has spoken by telephone to his counterpart in Jerusalem Ehud Olmert, urging the Israelis to fulfil their humanitarian obligations.
Israel's air force today targeted symbols of Hamas power in Gaza, striking a university linked to the Islamist group, a security compound and a house next to the home of Prime Minister Ismail Haniyeh.
More than 300 air strikes since Saturday have wreaked devastation on Gaza, killing 315 including civilians and children. Most of those killed since Saturday are reported to be members of Hamas security forces, but the UN agency responsible for Palestinian refugees said at least 51 of the dead were civilians.
The attacks have left more than 1,400 wounded, overwhelming hospitals and exacerbating shortages of fuel, food and medicines.
Israel says that the bombing is intended to stop a wave of rocket attacks on its territory, which today claimed their second victim in a strike on the city of Ashkelon which killed one man and wounded several others.
There are suspicions that Israel may be poised to launch a ground assault after its Cabinet approved a call-up of 6,500 reserve soldiers. The country has also doubled the number of troops on the Gaza border in the past two days, and deployed an artillery battery.
The United Nations Security Council yesterday issued a statement expressing "serious concern" at the escalation of the situation in Gaza and calling for "an immediate halt to all violence", while the European Union has also condemned the "disproportionate use of force" from both sides.
In his statement today, Mr Miliband said: "The Prime Minister and I are following developments in Gaza with grave concern. The rise in rocket attacks on Israel since December 19, and yesterday's massive loss of life, make this a dangerous moment which should be of concern to the whole of the international community.
"The UK supports an urgent ceasefire and immediate halt to all violence. The unanimous UN Security Council press statement overnight, and the EU's statement yesterday, rightly argue for this position.
"The deteriorating humanitarian situation is deeply disturbing. The Prime Minister has spoken to Prime Minister Olmert of Israel. As we made clear yesterday, Israel must abide by its humanitarian obligations.
"The UK supports the prompt and sufficient delivery of food, fuel and medicine into the Gaza Strip."
In an apparent expression of solidarity with Palestinian President Mahmoud Abbas, whose Fatah party holds power in the West Bank but has lost control of Gaza to Hamas, Mr Miliband said that support should be given to leaders who are committed to peaceful negotiations.
Arab leaders must make clear that the interests of the Palestinian people lie in the creation of a viable state alongside Israel, not in continuing conflict, he said.
"I have discussed this unfolding crisis with my counterparts in the region and beyond," said Mr Miliband. "There is a clear consensus, which we support, that everything should be done to protect the political space for those leaders committed to peaceful negotiations.
"I have discussed with Egyptian Foreign Minister Ahmed Aboul Gheit his plans to convene a meeting of Arab League Foreign Ministers.
"This is an important opportunity for Arab leaders to make clear that the interests of the Palestinian people can only be secured through a viable Palestinian state existing alongside a secure Israel. We must renew our collective effort to achieve this goal in 2009.
Palestinian chief negotiator Saeb Erekat this morning called for an immediate end to the Israeli attacks, a return to ceasefire in Gaza, access for humanitarian supplies and the restoration of dialogue between Hamas and Fatah.
Mr Erekat told BBC Radio 4's Today programme: "What Israel is doing deserves the strongest condemnation of the international community.
"At the end of the day you don't solve such problems with military means and such large-scale attacks."
But the Israeli deputy ambassador in London, Talya Lador-Fresher, denied the air strikes were indiscriminate. She told Today: "We have been targeting security institutions and we have been targeting Hamas.
"Both the targets and the majority of the casualties were people in uniform, Hamas operatives that were busy trying to launch rockets and doing terror attacks against Israeli citizens.
"We show restraint and even now we target the organisation. They are showing no restraint and are targeting civilians."
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