Labour leader Ed Miliband said David Cameron's "silence" on events in Gaza is "inexplicable".
Miliband criticised Israel's military offensive as "wrong and unjustifiable" and called on the government to produce a clear and united message on the crisis.
The Prime Minister is wrong not to have opposed Israel's incursion into Gaza.
His silence on the killing of hundreds of innocent Palestinian civilians caused by Israel's military action will be inexplicable to people across Britain and internationally.
We need the clear and unequivocal message that has not so far been provided to be sent from Britain to both sides in this conflict.
David Cameron and the Cabinet must put Britain in a leading role in pressuring both sides now to end the violence.
More top news
David Cameron will be facing a hostile audience when he meets with leaders from the remaining 27 EU nations this week, writes James Mates.
Baroness Warsi warns reports of hate crimes are rising after a "divisive" EU campaign largely focusing on immigration spurred street abuse.
Labour has descended into crisis as several high-profile members of the shadow cabinet have quit in the past few hours. Here's who they are.