Israel is committing war crimes in Gaza, several MPs including a former Cabinet minister have said.

Labour former Cabinet minister Peter Hain joined other Opposition MPs in condemning Israel's military offensive in Gaza, saying any other country would be regarded as committing war crimes.

Mr Hain also warned that hardline Islamic extremist group the Islamic State of Iraq and the Levant (Isis), currently brutally controlling territory across Iraq and Syria, could take control in Gaza unless Israeli negotiations with Palestine are successful and serious.

During a statement from David Cameron on the crisis, Mr Hain told the Prime Minister: "Surely friends of Israel like you and I have a duty at this time to speak the truth.

"These attacks, despite the horrendous rocket assault on Israel, despite that, and the extremism of Hamas, these attacks are not proportionate - in any other conflict they would be described as war crimes.

"That is the truth.

"And the problem also is there is no end in sight to this.

"What will happen is that a moderate Palestinian leadership having been replaced by Hamas through the failure to succeed in negotiations - Hamas, as the respected former Israeli government adviser Daniel Levy has suggested, could soon be replaced by Isis in Gaza.

"We have to start as the West speaking the truth, acting, and persuading the Israeli government to negotiate seriously."

Mr Cameron said he always speaks the truth with Israel, using the example of illegal settlements. But the Prime Minister said that if Hamas stopped attacking Israel with rockets then the occupation of Gaza would end.

But former Liberal Democrat leader Sir Menzies Campbell said Israel's response to Hamas's rocket attacks was disproportionate.

Sir Menzies said: "You asked what the reaction should be here were we to be subject to a degree of rocket attacks such as has been sustained by Israel.

"Can I tell you what I would ask, indeed what I'd demand as an MP? That our government should respond in a proportionate way, consistent with international law, and with proper regard for the safety of innocent men, women and children.

"Can it really be that Israel, with all of the sophisticated military technology at its disposal, can only protect itself by the kind of operations which the secretary general of the United Nations has called atrocious?"

Mr Cameron said he thought it was worth "putting yourself in the shoes for a minute of the Israeli people who have suffered these rocket attacks and who are quite sensibly asking their government to take action to stop them in future."

Labour frontbencher Richard Burden warned that Israel had a history of illegally using UK-supplied arms.

He said: "Will you agree with me that the targeting of civilians or the wilful disregard of the lives of civilians is a crime, whether those civilians are flying their civilian aircraft, whether they are sheltering in their homes in south Israel, or whether they are sheltering in their homes in Gaza?

"And are you aware that Israel has got a history of using UK-supplied arms and components, in contravention of the EU consolidated criteria.

"Would you consider Israel's use of British supplied arms or components in Gaza today to be in contravention of those criteria?

"Are you asking Israel whether they are or whether they are not? And what answer have you had?"

Labour veteran David Winnick (Walsall North) and the Green Party's Caroline Lucas (Brighton Pavilion) also condemned Israel's actions as war crimes, while Labour's Sir Gerald Kaufman (Manchester, Gorton) criticised Israeli prime minister Benjamin Netanyahu for claiming Hamas wants "telegenically dead" Palestinians.

But foreign affairs select committee chair Richard Ottaway said Israel had no alternative.

The Tory MP said: "Much has been made of what is or is not proportionate.

"The argument is being made that it should be an eye for an eye.

"But in truth in international law the response should be proportionate to the threat.

"Would you agree that actually Israel has no alternative but to go and find who is firing the missiles at them and to stop them?"

Liberal Democrat Bob Russell (Colchester) accused the Prime Minister of being "less than even handed" on the Gaza crisis, insisting the Israeli Defence Force may have committed war crimes and prosecution should be considered.

Mr Cameron said: "I support Israel's right to defend itself but that right has to be exercised in a proportionate way. That is what international law says."

Conservative Crispin Blunt (Reigate) said: "Last week... the death toll of Palestinian children in the conflict since 2000 stood at 1,430. Today it is reported at 1,472.

"When democracies depart from the rule of law they give legal and moral authority to our enemies. Israel is in consistent and today grievous breach of the Geneva Conventions. What are you doing to bring Israel back within the rule of law?"