America and France clashed openly yesterday over the proposed United Nations ceasefire plan which is opposed by Lebanon and other Arab states.

US and French teams at the UN headquarters in New York returned to the drawing board to devise a fresh draft resolution, but the mood among diplomats was pessimistic. One diplomat described the situation in Lebanon as "intractable" and warned that there was no plan B if a resolution could not be thrashed out fast.

The French president, Jacques Chirac, broke from his holiday to deliver an implicit rebuke to Washington. Mr Chirac warned the Bush administration that an immediate ceasefire was the only solution to the conflict and said giving up on this was "immoral". He urged the US to speed up its response to Arab nations' demands for changes to the ceasefire plan.

"It appears today that the Americans have reservations about adopting this project, but I don't want to imagine there not being a solution." He added: "To accept the present situation and renounce an immediate ceasefire would be the most immoral of solutions."

The difficulty of finding a diplomatic solution was also underscored when Hassan Nasrallah, the Hizbullah leader, in his first comments on the original UN draft, rejected it. "The least we can describe this [draft resolution] is as unfair and unjust. It has given Israel more than it wanted and more than it was looking for," he said.

Diplomats at the UN said that even if the US and France were able to agree a new draft, the security council could not vote on it until tomorrow at the earliest.

The Washington-Paris rift is over the withdrawal of Israeli forces from southern Lebanon. The US is backing Israel's position that the proposed deployment of the Lebanese army in the south is insufficient: the Israelis say the Lebanese army is not strong enough to deal with the Hizbullah militia and it needs the support of an international force. The French team argues that the deployment of the Lebanon force is a good first move and that it would take weeks, or months, to deploy the international force.

The French and US governments have been struggling for more than a week to find a draft resolution that stands a chance of securing a ceasefire. The US, France and Israel agreed at the weekend on a draft, but underestimated the level of opposition from Lebanon and the Arab states.

Lebanon protested that, under the draft resolution, Israel would be allowed to stay in southern Lebanon for an undefined period and could take "defensive" action against Hizbullah. Dan Gillerman, Israeli ambassador to the UN, said: "I do not see any bridging of the disagreements ... they had both agreed on a document, [but] the French at the moment seem to have had second thoughts, which are so wide apart [from the US] that a lot of work will have to be done to turn the document into a viable resolution."

Israeli diplomats have said they will stop fighting within days of a ceasefire resolution being adopted. But one Israeli diplomat said the government was happy to see negotiations bogged down because it gave it longer to continue its offensive.

David Welch, the US state department assistant secretary, gave no ground when he visited the Lebanese prime minister, Fouad Siniora, in Beirut yesterday, the first US visit since Condoleezza Rice was told last week in the aftermath of the Qana bombing she would not be welcome in the Lebanese capital. According to a Lebanese official, Mr Welch told Mr Siniora that Israel would not withdraw until the international force was in place.

Mr Welch also met Nabih Berri, the speaker of the Lebanese parliament who acts as a conduit for Hizbullah. He said afterwards: "Mr Welch, as I expressed to him, is a skilful embellisher for an ugly resolution and, therefore, I agree with prime minister Siniora by saying that there is no progress until now."

Hopes at the UN are pinned on a two-stage process, with two UN resolutions - a cessation of hostilities, followed by an international force - on a timescale tight enough to placate both sides. Britain appeared to playing little role in the negotiations, amid claims at the UN that Tony Blair has angered France and other European nations by taking a strongly pro-Israel line with George Bush in private.

Casualties

Lebanon yesterday

Hizbullah: 3 killed

Civilians: at least 8 killed

To date

Hizbullah: 98 killed (IDF claim 400)

Civilians: 1,005 killed

Israel yesterday

Military: None (Lebanese claim 11)

Wounded: None reported

To date

Military: 63 killed

Civilians: 35 killed

All figures revised daily and based on Lebanon and Israel government estimates.