Labour leader Ed Miliband has accused David Cameron of failing to speak out about an Israeli military operation that he describes as “wrong and unjustifiable”.
In a strongly worded statement, he said Mr Cameron had been right to call Hamas an appalling, terrorist organisation.
“But the Prime Minister is wrong not to have opposed Israel’s incursion into Gaza”, said Mr Miliband.
The Opposition leader added: “And his silence on the killing of hundreds of innocent Palestinian civilians caused by Israeli’s military action will be inexplicable to people across Britain and internationally.”
Downing Street reacted angrily to the statement, insisting the Prime Minister had been clear that both sides in the conflict need to observe a ceasefire.
“We are shocked that Ed Miliband would seek to misrepresent that position and play politics with such a serious issue.”
A Labour source said the situation on the ground in Gaza had led Mr Miliband to speak out.
He said he supported Israel and believed it had the right to defend itself.
“But its military actions in the past two weeks have been wrong and unjustifiable.
“The escalation of violence engulfing Gaza has led, and is leading, to suffering and destruction on an appalling scale, and is losing Israel friends in the international community day by day.”
It came amid claims that Britain is selling arms to Israel that could be being used against Palestinian citizens.
Katy Clark, a Labour MP on the Committee on Arms Export Controls, told Sky News arms had been sold since 2010 under hundreds of licences that were still in place.
Her committee found the UK can sell 22 different types of equipment to Israel including components for military combat vehicles, communications equipment, sniper rifles and water cannon.
The Government said it had started a review into all the licences, with the ultimate decision to suspend any lying with the Department for Business, Innovation and Skills.
It is led by Lib Dem minister Vince Cable, who will be under pressure to act given the outspoken interventions from senior figures in his party.
Nick Clegg, the Deputy Prime Minister and Lib Dem leader, has called on Israel to open direct talks with the political arm of Hamas.
Writing in the Guardian, he said the “daily images of human torment in Gaza have been harrowing and heartbreaking”.
And insisted that Israel’s “disproportionate” military response was only worsening the long-term situation.
Mr Clegg pointed to how the Queen shook hands with the former IRA commander Martin McGuinness as a reminder “that even the most intractable conflicts can be resolved”.
And Paddy Ashdown, the former leader, said that any arms sales contributing to this conflict should be stopped.