Condoleezza Rice tonight warned that an immediate ceasefire in the Middle East would be a false promise unless the underlying causes of the violence were addressed.

The US Secretary of State spoke after Britain and the United States found themselves isolated and under fire at the United Nations Security Council for blocking a concerted international call for an end to the hostilities.

"We do seek an end to the current violence and we seek it urgently," said Ms Rice, who is leaving for the Middle East after the weekend for a round of diplomacy that will include visits to Israel and Italy.

"More than that, we seek an end to the root cause of the violence so that an enduring peace can be established.

"But if we look for a ceasefire that simply freezes the status quo ante, then we will be back here again in another six months, or nine months, or a year, looking for another ceasefire as Hezbollah uses southern Lebanon as a base to launch rockets against Israel."

Several hours earlier, Britain and the United States proposed a UN statement vowing to prepare conditions for a ceasefire, in the face of growing pressure to halt the fighting.

Criticism has mounted that the two countries are blocking the 15-nation Security Council from endorsing the UN secretary-general’s call for an immediate suspension of fighting.

More than 300 Lebanese civilians and nearly 30 Israelis have died since the fighting started, and half a million Lebanese civilians have been displaced. Israel has warned that it is now preparing a ground invasion to eradicate Hezbollah strongholds in the south of Lebanon, a move that can only add to the misery of the civilian population.

The British and American proposal called for the Security Council to express its intention "to create the conditions for a permanent solution and to bring about an immediate end to hostilities." It also called on all sides to exercise restraint and to allow humanitarian access.

Ms Rice put the blame for the current crisis on the shoulders of Hezbollah. "In UN Resolution 1559 the world calls for the government of Lebanon to be allowed to function as a sovereign government without the intervention of foreign powers. That is why Syrian forces were asked to leave Lebanon," she said.

"The government of Lebanon needs to be able to extend authority over the whole of its territory. You can't have a situation where the south of Lebanon is a haven for unauthorised armed groups that sit and fire rockets into Israel, plunging the whole country into chaos, when the Lebanese government didn't even know what was going to be done."

Britain too says that the focus of international diplomacy must be on what action can be taken to bring about a "durable" ceasefire. Tony Blair intends to discuss the Middle East crisis with President Bush at the White House in a week's time, on July 28, it emerged today.

Other countries do not agree with the US and British analysis. France, by contrast, has called for an "humanitarian truce" to alleviate the suffering of civilians as soon as possible. It has proposed that the Security Council call for a ceasefire, while addressing the underlying causes of the conflict.

Russia, Greece, Congo, Peru and Qatar, the sole Arab representative on the Security Council, have all also endorsed the need for an immediate cessation of hostilities. Qatar has accused council-members of "vacillating" and called for a Security Council resolution as soon as possible.

Jan Egeland, the UN’s emergency relief coordinator, today reiterated Mr Annan's appeal for a ceasefire as he briefed the Security Council this afternoon on what he described as a worsening humanitarian crisis. "The war, the terror, the attacks on civilans and civilian infrastructure has to stop in Lebanon, northern Isreal and Gaza," he said.

But Vijay Nambiar, the leader of the UN mediation team in the Middle East, warned the Security Council that there remained serious obstacles to a comprehensive ceasefire, and that efforts should focus on securing some form of cessation of hostilities.

"This is essential so that captives are protected and released, humanitarian access is assured, civilian casualties are dramatically reduced, and the political space is opened to negotiate a full and durable ceasefire," he said.

Mr Nambiar said that Israel had told the UN team that the violence "was not, as in the past, a response to a particular incident - the abduction of the two soldiers - but was definitive response to an unacceptable strategic threat by Hezbollah, and a message to Iran and Syria that threats by proxies would not longer be tolerated".

Israel, meanwhile, agreed to a "humanitarian corridor" for people fleeing Lebanon, diplomats said.

"We have asked for humanitarian corridors," said Jean-Marc de La Sabliere, France’s UN ambassador, said. "We have a partial answer. We understand that there is an agreement from the Israelis to ahve a corridor to go out of Lebanon. Still the question is to have a corridor inside, to have corridors for food supplies and health services."

Mr Annan’s six-point peace plan calls for an "enlarged peacekeeping force", to help the Lebanese army move into the south. He also calls for an international conference to disarm Hezbollah.

Rowan Williams, the Archbishop of Canterbury, today urged Mr Blair and Mr Bush to change their minds and back the UN's call for an immediate ceasefire. The Pope has also called for a cessation of hostilities.

Dr Williams warned the British and US governments that they would have to reckon with a rising level of public despair and dismay at the escalating conflict.