Addressing an emergency meeting of the UN Security Council, UN Secretary General Antonio Guterres was not mincing his words: "Madam President, excellencies. Hell is breaking loose in Lebanon. As I told the General Assembly yesterday, we should all be alarmed by the escalation. Lebanon is at the brink."

Mr Guterres said Monday saw Lebanon's biggest loss of life in a single day in a generation.

Both Israel and Hezbollah were blamed for the worsening situation.

Britain's foreign secretary was among many speakers calling for a diplomatic solution.

"We are on the precipice," he told the meeting. "The rockets must stop now. The airstrikes must stop now. Talks must start now."

Follow latest: US calls for 21-day ceasefire

But outside the chamber there was an ominous warning from Iran's representative that his country may become more involved in this war if it goes on.

"Let me be frank," Abbas Araghchi, Iran's foreign minister told reporters. "The region is on the brink of a full scale catastrophe. If unchecked, the world will face catastrophic consequences unlike anything before.

"Iran firmly upholds its inherent right to defend its vital interests."

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Israel's ambassador Danny Danon fought back in the meeting, singling out Iran for blame in this crisis.

"Every missile fired by Hezbollah, every drone launched by Iranian proxies, every act of terror on foreign soil, traces back to one source: the Islamic regime of Iran.

"It is the spider at the centre of this web of violence, and until that web is dismantled, there can be no peace in the region."

The crisis has overshadowed events at the UN General Assembly. The fear here is of an escalation engulfing the region in an even bigger conflict.

The US is leading efforts to push for a ceasefire. Its diplomats have told Sky News they are speaking directly with Israel and indirectly bringing pressure to bear on Iran and Hezbollah through third countries.

What is not clear is if there is the time to contain events that are spiralling quickly out of control.