Archbishop of Canterbury Rowan Williams has joined calls for the UK to press for a ceasefire in the Middle East.
"We really have to ask whether some Western governments are catching up with the consciences of their own people", he told BBC Radio 4.
British Foreign Secretary Margaret Beckett has so far refused to condemn Israel's response to rocket attacks from militants in Lebanon.
But Archbishop Williams said the UK and US must change their stance.
Israel continued its military offensive in Lebanon by bombing more than 40 targets, mainly in southern Beirut early on Friday.
Hezbollah's leader Hassan Nasrallah has appeared on TV, saying Israel has not dented the group's capabilities.
Archbishop Williams told BBC Radio 4's Today programme calls for an immediate ceasefire might not work but the violence was not going to stop without them.
"The major players in this at the moment who are not supporting a ceasefire - our own government and the United States government - maybe perhaps have to reckon with a rising level of public despair and dismay at the spiral continuing," he said.
"And I hope very much that they will bring their influence to bear in moving towards a ceasefire."
UN Secretary General Kofi Annan has called on Israel and Hezbollah to bring hostilities in Lebanon to a swift end.
The US and UK have condemned Hezbollah (not Lebanon as stated in earlier versions of this story) but not Israel, saying only that there should be a "proportionate" response to Hezbollah's attacks.
On Thursday, Mrs Beckett repeatedly resisted pressure from MPs for her to condemn Israel's actions.
Ex-Labour Foreign Office Minister Chris Mullin asked her if it wasn't "a tiny bit shameful that we can find nothing stronger than the word regret to describe the slaughter and misery and mayhem that Israel has unleashed on a fragile country like Lebanon".
Mrs Beckett said she had "stringently condemned" Hezbollah but she had also tried to be "relatively proportionate" in what she said about all other players in the crisis.
"I can assure him that I am striving in every way that I can to act in a way that will be effective to bring about the situation that he desires," she said.
But the most effective action would not always be the same as what people wanted her to do.
And Hezbollah held the "simplest levers" to ending the conflict, by releasing captured Israeli soldiers, she said.
The exchanges came as the UK pledged £2m towards relief efforts in the Lebanon after an appeal by the Lebanese prime minister.
Shadow foreign secretary William Hague said he thought "elements of Israel's response are disproportionate".
Mr Hague told MPs the right of Israel to defend itself was "clear" and calls for an unconditional Israeli ceasefire were "futile" unless rocket attacks on it stopped and captured soldiers returned.
But the Tory frontbencher said Israel's "disproportionate" response was delaying efforts to bring about a ceasefire.
Former Labour Cabinet minister Clare Short accused ministers of "inflaming" the situation by pursuing an "unbalanced and morally wrong" policy.
Ms Short told the Commons "massive killing of innocent Lebanese civilians and destruction of infrastructure" was so disproportionate that it amounted to a war crime.
Liberal Democrat spokesman Michael Moore said an urgent ceasefire was needed to stop the crisis spiralling around the world.
Even the perception that the US was willing to give the green light to Israeli military action for a few more days was deeply damaging, added Mr Moore.