The US secretary of state, Condoleezza Rice, today ruled out a ceasefire as a solution to the conflict in the Middle East.

Ahead of her weekend trip to the troubled region, she dismissed a ceasefire - proposed by the UN secretary general, Kofi Annan, among others - as a "false promise".

"An immediate ceasefire without political conditions does not make sense," she said.

With tensions rising at the Israeli-Lebanese border, Ms Rice said she hoped her trip would create conditions for a lasting Middle East peace, but admitted the diplomatic work would be difficult.

Outlining US plans for a diplomatic solution to the current crisis in Lebanon, the secretary of state also defended her decision not to talk to officials from Hizbullah or Syria.

"Syria knows what it needs to do and Hizbullah is the source of the problem," she said at the state department in Washington.

Ms Rice said she would work with US allies in the region to help create conditions for "stability and lasting peace". She said she was meeting both the Israeli prime minister, Ehud Olmert, and the Palestinian president, Mahmoud Abbas. She will also meet US allies and Lebanese officials at a gathering in Rome.

The secretary of state said the Lebanese government would need "robust" international assistance to take control of the south of the country from Hizbullah. But she said US ground forces were not likely to be part of any expanded international peace force in Lebanon.

At least 319 people have been killed in Lebanon by the Israeli campaign, according to Lebanese security officials. At least 34 Israelis have been killed, including 19 soldiers. Early today, one air force officer died and three were injured when two Israeli helicopters collided near the Lebanese border.

Asked why she had not gone to the Middle East earlier to try to end the death and destruction in the region, Ms Rice said: "I could have gotten on a plane and rushed over and started shuttling, and it wouldn't have been clear what I was shuttling to do."

Despite Israel's ongoing preparations for a ground offensive, she said she took the Israeli government at its word when it said it had no desire to widen the conflict.

The Israeli military earlier warned hundreds of thousands of people in southern Lebanon to flee. Its planes dropped leaflets telling residents to clear the area after officials met to decide how big a force to send in, according to senior military officials.

The officials said Israel would not stop its offensive until Hizbullah was forced behind the Litani river, 20 miles north of the border, creating a new buffer zone in a region that saw Israeli occupation between 1982 and 2000. Reservists in northern Israel were ordered to report for duty.

Daniel Ayalon, the Israeli ambassador to Washington, said Israel would not rule out an international peacekeeping force in Lebanon. But he said Israel was first determined to take out Hizbullah's command and control centres and weapons stockpiles.

He described the conflict as a "mop-up" operation and said that Israel had no desire to repeat its 18-year occupation of southern Lebanon that ended in 2000.

"They overplayed their hand, they miscalculated," Mr Ayalon said of Hizbullah militants based in southern Lebanon.

Israel's military chief said today the country's forces had killed nearly 100 Hizbullah fighters in Lebanon during the 10-day offensive. Lieutenant-General Dan Halutz said at least 13 Hizbullah guerrillas were killed yesterday alone in fierce fighting just inside southern Lebanon. Four Israeli soldiers were killed in those clashes.

Hizbullah, on the other hand, said earlier today that two of its fighters had been killed in the latest fighting with Israeli troops, bringing to five the number of guerrillas killed.

Israel launched its military campaign against Lebanon and the militant Shia Muslim group on July 12.