Foreign Secretary David Miliband has voiced "grave concern" over the massive loss of life in the Gaza Strip as Israeli air strikes on the Palestinian enclave continued for a third day.
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 has 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.
In his statement, 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 (Sunday'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.