Israel called up five battalions of army reservists today and dropped leaflets across southern Lebanon warning civilians to leave towns and villages and head north towards Beirut as it prepared for a major ground offensive against Hezbollah positions.

The preparations for ground war came as 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.

Britain and the United States have 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, the US Secretary of State, 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.

Israel has so far failed to stop Hezbollah cross-border rocket attacks despite its 10-day bombardment, which has killed 345 people in Lebanon, forced half a million to leave their homes and destroyed many of the country’s vital installations.

Hizbollah rockets crashed into the northern Israeli city of Haifa on Friday, wounding 19 people. Other towns were also hit. Rocket attacks have killed 15 civilians in Israel, which has also lost 19 soldiers in the conflict.

Lebanese families with possessions packed into cars and pickup trucks clogged roads to the north after Israeli planes dropped leaflets warning residents of south Lebanon to flee for safety beyond the Litani river, about 20 km (13 miles) from the border.

An estimated 300,000 mostly Shia Muslim Lebanese normally reside south of the Litani. There was no word on how many have already fled the bombing and fighting of the past few days. Air raids have wrecked many roads and bridges in the region.

"The siege on Lebanon is not letting humanitarian aid in,", said Hisham Hassan, spokesman for the International Committee of the Red Cross (ICRC)."The south is isolated."

Two ICRC trucks were on their way from Beirut to a hospital in Tyre, where staff began burying corpses temporarily in a mass grave dug in an army barracks to clear space in the morgue.

An Israeli military source said the army had told 3,000 reserves to report for duty. The call-up came a day after Defence Minister Amir Peretz spoke of a possible land offensive.

"Let no terror organisation feel we would cower from any operation," he said. "We have no intention of conquering Lebanon but if we have to act to complete our tasks and reach a victory we will do it."

Lebanon warned that its army will go into battle if Israel invades the country - a defiance which analysts warn bears little relationship to military reality.

But Elias al-Murr, the Defence Minister, told al-Arabiya television that the army would have to fight back during any land invasion. "Our constitutional duty is to defend Lebanon as a Lebanese army. This is our role," he said.

The Israelis have been using radio broadcasts and even text messages to urge the inhabitants of southern Lebanon to move past the Litani river, about 25 miles north of the Israeli border.

About 800 foreigners were evacuated by sea from the southern city of Tyre, leaving Tyre's remaining inhabitants fearing the worst. "The foreigners have gone. That means the war will really begin now," said Hassan Bazzi, a port worker.

Mr Annan has given the UN Security Council a six-point peace plan to be implemented as soon as hostilities cease. It calls for a beefed-up international force to help a strengthened Lebanese army to take over the south of the country from Hezbollah.

It also envisages the surrender of captured Israeli soldiers by Hezbollah to the Lebanese Government under Red Cross supervision, formal Lebanese recognition of the "blue line" border with Israel, a pledge of aid and an international mechanism to oversee the agreement. An international conference would set deadlines for disarming Hezbollah.

Hassan Nasrallah, the Hezbollah leader, said that he would only release the soldiers as part of a prisoner swap. He claimed Israel's claims to have hit half of Hezbollah's missile potential and arsenal were wrong and warned of "more surprises" to come.

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