The UK expressed "deep concern" today after Israeli airstrikes killed more than 150 people in the Gaza Strip.

The Foreign Office urged both Tel Aviv and Palestinian leaders to pursue "peaceful means" of reaching a settlement amid signs that tit-for-tat clashes were spiralling out of control.

"The only way to achieve lasting peace in Gaza is through peaceful means," a spokesman said.

"Whilst we understand Israeli's obligation to protect its population we urge maximum restraint to avert further civilian casualties. We also call on those in the Gaza Strip to immediately cease all acts against Israel."

Prime Minister Gordon Brown said he was "deeply concerned" by continuing missile strikes from Gaza on Israel and by Israel's response today.

Mr Brown called on Gazan militants to cease all rocket attacks on Israel immediately, saying they were designed to cause random destruction and to undermine the prospects of peace talks led by President Abbas.

The Israeli military said the strikes by F-16 bombers were in response to an escalation in rocket attacks from Gaza over recent days, since a truce between the two sides expired.

The targets had been "Hamas terror operatives", training camps and weaponry storage warehouses, according to a statement.

Gaza officials reported more than 150 dead and 200 others hurt a result of the strikes - the most intense on the territory for decades.

A White House spokesman said the United States "urges Israel to avoid civilian casualties as it targets Hamas in Gaza".

Aid agencies working in Gaza called on Israel, Hamas and other Palestinian militant groups to pull back from the brink of an all-out military confrontation.

The agencies - Oxfam, CARE International, CAFOD, Medico International and Diakonia - said military action would leave a humanitarian catastrophe in its wake.

Jeremy Hobbs, director of Oxfam International, said: "Gaza has already been paralysed by the Israeli blockade.

"A military attack on Gaza could completely destroy essential infrastructure for sewage treatment, water provision and electricity for hospitals and homes, with devastating impact on civilians.

"Our governments need to help all parties to the conflict find a genuine and lasting solution.

"A military offensive will hit ordinary people, the very people we need as partners in building a better future for the region.

"Military action would alienate Gaza further and the consequences of this would be disastrous."

Martha Myers, of CARE International, said: "There is no military solution to the situation and the upsurge in violence destroys hopes for peace, refuelling the cycle of violence.

"There is simply no alternative to negotiations to address the root causes of the conflict."

Liberal Democrat foreign affairs spokesman Ed Davey branded the bombings "disproportionate" and "unacceptable".

"The danger is that this will spark a new spiral of violence and terror, when what is really needed is an international effort to restore the ceasefire," he added.

"Israel knows the international community condemns the attacks by Hamas, but it should also realise from the past that this sort of mass attack will only postpone the peace Israel, and the region, needs."

Shadow Foreign Secretary William Hague said: "We deeply regret the loss of civilian life in Gaza today. We call on the Israeli government to show restraint.

"At the same time we call on Hamas to stop the rocket attacks which are an unacceptable threat to Israel's security, so that the ceasefire, which Hamas failed to renew, can be urgently restored."

The British Muslim Initiative said it condemned unreservedly what it described as "the criminal and barbaric Israeli air strikes launched against the beleaguered Palestinian nation".

In a statement, BMI said: "These attacks which killed more than 155 civilians, including many children, can only be described as clear crimes of war against an innocent, defenceless and besieged nation, who has been surviving without basic living amenities, food, medicine and fuel for more than a year and a half."

BMI said it also condemned the "shameless silence of Western and Arab governments towards the continued violations and crimes committed by Israel and its agents and their collective contempt towards international law, as well as all notions of humanity, reason and rational".

Together with a number of British organisations, BMI called for a demonstration outside the Israeli Embassy in London tomorrow.

BMI President Mohammed Sawalha said: "Governments have continued to fail the Palestinian people, and hundreds if not thousands have been slaughtered as a result. The people of the world however will never stay quiet, nor will they ever forget."

Conservative leader David Cameron told Sky News: "Obviously the pictures on our television screens are pretty horrific and all civilian casualties are a matter of great regret so I hope that both sides will show restraint.

"Everyone understands that Israel has a right to defend herself and she has been attacked by rocket attack after rocket attack.

"We need both Israel to show restraint and also the militants in the Gaza Strip to stop firing rockets.

"In the end the only progress will be political progress and a settlement between the Israelis and the Palestinians and that is what's desperately needed."