Tony Blair has denied there is a Cabinet split on the Middle East, as it emerged Jack Straw has attacked Israel's "disproportionate" offensive.
Commons leader Mr Straw - who was foreign secretary until May's cabinet reshuffle - said Israel risked escalating a dangerous situation.
Downing Street said Mr Blair would not endorse or criticise the remarks.
He said a ceasefire could be achieved within days if the international community acted with urgency.
The prime minister's official spokesman insisted Mr Blair - who is in California meeting business leaders - was focusing his energies on solving the problems in Lebanon and wished to retain his influence.
In his statement, Mr Straw warned that a continuation of Israeli military action in Lebanon "could further destabilise the already fragile Lebanese nation".
Mr Straw backed Foreign Office Minister Kim Howells - who last weekend described the Israeli action as "disproportionate" - while adding that Israel had a right to defend itself "proportionately".
In addition, newspaper reports on Sunday suggested ministers have pressed Mr Blair to break with the US position and condemn Israel's response.
However, the Lord Chancellor Lord Falconer said there had been a "non-divisive discussion" about the way forward in the crisis at a Cabinet meeting on Thursday.
"We are all as supportive as we can be of trying to bring the thing to an end," he told the BBC's News 24 Sunday programme.
"I've read what Jack says and Jack gives a balanced account of what's going on and he says, like all of us, we're looking for a durable ceasefire that has some prospect of lasting."
The Cabinet was united behind achieving "a ceasefire right across the area that stops the appalling things that we're seeing", he added.
Foreign Secretary Margaret Beckett called Sunday's Israeli strike on Lebanon, in which at least 34 children died, "appalling".
However she told Sky News that the Cabinet was not divided over not calling for a ceasefire.
"There's not a single person in the Cabinet who is not desperately anxious about the situation...and agonising over whether we are in fact doing everything we can.
"Everyone is united on that point of view round the Cabinet table as they are in the international community right around the world."
Mr Blair has come under pressure from within his own party for not calling for an immediate ceasefire in southern Lebanon, but said that was not the solution to the crisis.
"If we can achieve a basis for a ceasefire that will allow Israel's security to be protected and the international community to be engaged in sorting out the south of Lebanon... then of course that's the right way to proceed," he told BBC political editor Nick Robinson.
But, he added, for any truce to work both Israel and Hezbollah had to be engaged in it.
"It cannot be that Israel stops taking the action it's taking but Hezbollah continue to kill, kidnap, and launch rockets into the north of Israel at the civilian population there," he said.
He wants the UN to agree a resolution to end the fighting, and send an international force of peacekeepers to southern Lebanon.
Mr Blair said if an agreement could be "endorsed by the governments of Israel and Lebanon" and could be "encapsulated in a UN resolution", the conflict could be stopped.
He added this "could happen in days if the international community is willing to act with the urgency I want it to act with".
When asked if the events in the Middle East put Britons in danger of further terrorist attack, Mr Blair responded: "When people stand up and fight, people will come after you."
Labour MP David Winnick welcomed Mr Straw's public criticism of the Israeli response.
The UN has called for a three-day truce between Israel and Hezbollah
"I think these comments reflect the majority view in the Parliamentary party, including ministers.
"Perhaps more importantly it's the view in the country at large."
He added that "sensible people" had no time for Hezbollah, but Israel's actions were merely encouraging extremists.
The Israeli assault began after Hezbollah captured two Israeli soldiers and killed eight in a cross-border raid on 12 July.
Some 600 Lebanese, the majority civilians, have been confirmed killed in the conflict. Fifty-one Israelis, including at least 18 civilians, have been killed, mostly by Hezbollah rockets.
The prime minister, who held talks with President Bush at the White House on Friday, is now spending several days in California promoting his climate change plans and UK hi-tech business.