A 21-day temporary ceasefire between Israel and Hezbollah in Lebanon is being discussed by the US and France as a way of ending the crisis, French foreign minister Jean-Noël Barrot has told the UN security council.

The plan came as the UN secretary general, António Guterres, warned that “hell is breaking loose” in the country, and the UK foreign secretary called for an immediate ceasefire, a joint statement on which the US has not endorsed.

Israel’s top general has said the country is preparing for a possible ground operation into Lebanon after an intense three-day bombing campaign that has killed more than 600 people.

The French initiative was announced at an emergency meeting of the security council on Wednesday and reflects the tensions between the US and its European allies, notably the UK and France, on how to press Israel to end its bloody offensive inside Lebanon. The UK and France had been calling for an immediate ceasefire.

The US deputy envoy Robert Wood said Washington’s plans would be unveiled in the coming days and would require a real and effective mechanism enforcing the blue line, the UN-drawn provisional border between Israel and Lebanon.

He said “we are working with other countries on a proposal that we hope will lead to calm, discussions and diplomatic solutions.”

There has been tension between the US and its European allies about whether to call for an immediate ceasefire at the security council. The UK foreign secretary David Lammy backed an immediate ceasefire, saying it was time to pull back from the brink, adding “a full blown war is not in the interests of Israeli or Lebanese people”.

He said nothing justified Hezbollah’s attacks and urged Iran to use its influence to persuade Hezbollah to agree to a ceasefire.

But US diplomats indicated an unconditional ceasefire call in the form of a joint security council statement could be seen as accepting a moral equivalence between the behaviour of Israel and Hezbollah, a group that is labelled a terrorist group by the US.

In a bid to resolve the differences, US President Joe Biden met French president Emmanuel Macron on the sidelines of the United Nations general assembly in New York “to discuss efforts to secure a ceasefire between Israel and Lebanese Hezbollah and prevent a wider war”.

Iranian foreign minister Abbas Araqchi told the UN security council the US and UK’s “unwavering support for Israel has given them carte blanche for all sorts of sinister behaviour”.

“Without a ceasefire in Gaza there will be no guarantee for peace in the region,” he added. “The international community cannot afford to remain silent … the UN security council … must shoulder its responsibility and respond decisively.”

Lebanese prime minister Najib Mikati said his country was witnessing an “unprecedented escalation” and that hospitals were overwhelmed. “The aggressor is claiming that they are only targeting combatants and weapons, but I assure you that the hospitals are full of civilians,” he said.

The proposal for a temporary three-week cessation of hostilities might provide a platform to reopen stalled talks on the discussions over a ceasefire between Hamas and Israel in Gaza. Hezbollah has said it will stop its strikes if Hamas agrees to a Gaza ceasefire, but there is no sign currently of either the Hamas leadership or the Israeli prime minister Benjamin Netanyahu coming to an agreement.

Netanyahu was due to arrive in New York on Thursday, and is expected to set out whether he supports a 21-day break in hostilities.

Wood said “diplomacy will only become more difficult” if the conflict escalates further, adding he was gravely concerned by reports that hundreds of Lebanese civilians had died in recent days.

But he insisted the origin of the conflict was the hundreds of thousands of Lebanese civilians, and 65,000 Israeli civilians, who have been displaced due to Hezbollah’s decision on 8 October to break the peace that has largely endured.

He said that no one wanted to see a repeat of the war in 2006, adding “the war must end with a comprehensive undertaking that has real implementation mechanisms”.

No details of the implementation mechanisms were set out by the US envoy, but it is not likely to be backed by Hezbollah if it infringes on its sovereignty.