Mr Brown has spoken to leaders on both sides of the conflict
UK Prime Minister Gordon Brown has called for an urgent ceasefire in Gaza amid a "humanitarian crisis" in the Palestinian territory.
His plea came after the UK pledged to give £6.9m in emergency aid for those caught up in the violence.
The EU and UN have called for the violence to end while the US has said Hamas, which controls the Gaza Strip, should commit to a truce.
Hundreds have died during the conflict between Israel and Gaza.
Israel has rejected calls for a 48-hour halt to its military action while it continues to come under attack itself from militants in Gaza.
The attacks are now in their fifth day with reports of more than 370 Palestinians and four Israelis dead.
Ministers said food, fuel and medicine were "desperately needed" and aid agencies must have unrestricted access to those in need.
Mr Brown said aid was now getting through to the Palestinian territory.
"It is vital that moderation must now prevail - there's a humanitarian crisis."
He said he had spoken on the telephone to the prime minister of Israel, Ehud Olmert, and received assurances that humanitarian aid would be able to get through and help casualties in Gaza.
Mr Brown said: "We have now set aside $10m of aid so that will happen.
"I have some indication that aid is now getting through.
"Of course, the second thing we've got to do is secure an immediate and urgent ceasefire."
United Nations aid workers are expected to go into the territory with supplies on Thursday.
Mr Brown said he had talked to leaders on both sides about a set of proposals put forward for the Palestinian territory and these were currently being discussed by the Arab League.
"I believe that this is the best opportunity for a ceasefire and for peace.
"I believe that the various forces involved should seize this opportunity now," he said.
Earlier International Development Secretary Douglas Alexander said the UK had urged the Israeli authorities to give aid agencies "unfettered access" to Gaza to help those in need.
He reiterated calls for a permanent ceasefire and said the UK was "highly engaged", along with the US and its Middle East partners, in trying to bring the conflict to an end.
However, UK and EU efforts to mediate a ceasefire have been attacked in some quarters as ineffective.
The Liberal Democrat's Richard Younger-Ross, a member of the Commons Defence Committee, has called for the House of Commons to return early from its Christmas break.
He has written to the Leader of the House Harriet Harman calling for Parliament to be recalled on Monday so it can debate the crisis.
Politicians are not due back until 12 January.
Meanwhile Archbishop of Canterbury, Dr Rowan Williams, called for politicians, including President-elect Barack Obama, to take more action to broker peace.
"We must unite in urging all those who have the power to halt this spiral of violence to do so.
"Those raising the stakes through the continuation of indiscriminate violence seem to have forgotten nothing and learned nothing
"It must surely be clear that, whilst peace will not wipe out the memory of all past wrongs, it is the only basis for the future flourishing of both the Israeli and Palestinian peoples."
A coalition of 20 Muslim and non-Muslim groups has said it will hold a demonstration in London on Saturday against what it calls Israel's "barbaric attacks".
Seventeen people were arrested during protests outside the Israeli Embassy in London on Sunday and Monday.
Further protests took place outside the embassy on Wednesday.