Sir Keir Starmer called on Israel and Hezbollah to agree an immediate ceasefire as he urged Britons to leave Lebanon immediately to escape the escalating violence.
The Prime Minister addressed the UN Security Council with a plea for an end to the violence in both Lebanon and Gaza.
In a blunt message to Israel he said Benjamin Netanyahu’s government needed to do more to ease the humanitarian crisis in Gaza.
The UK has deployed 700 troops to Cyprus to prepare for a possible evacuation of thousands of Britons.
Sir Keir urged Britons to leave by the remaining commercial routes without relying on a possible evacuation.
Ahead of his appearance at the UN in New York, Sir Keir said: “In relation to Lebanon, I am very worried about the escalation.
“I’m calling for all parties to step back from the brink, to de-escalate. We need a ceasefire so this can be sorted out diplomatically.
“But I have a very important message for British nationals in Lebanon which is: the time to leave is now.
Sir Keir Starmer gives a media interview ahead of addressing the United Nations General Assembly in New York (Leon Neal/PA)
“The contingency plans are being ramped up but don’t wait for those, there are still commercial flights.
“It’s very important that they hear my message, which is to leave and to leave immediately.”
At the UN Security Council he called on all sides in the disputes in the Middle East to seek a diplomatic solution.
He said: “We must address the situation in Gaza. October 7 was the bloodiest day for the Jewish people since the Holocaust.
“I utterly condemn the terrorist actions of Hamas. The ordeal of the hostages and their loved ones continues almost a year later.
“Six of them were killed in cold blood just a few weeks ago. So, I say again: let the hostages go.
“And we must face up to the humanitarian catastrophe in Gaza that continues to deepen by the day.
“Israel must grant humanitarian access to civilians in line with its obligations under international humanitarian law. There can be no more excuses.”
He added: “I call on the Security Council to seek political solutions that can break repeating cycles of violence like that in the Middle East. The region is at the brink.
“We need an immediate ceasefire between Israel and Lebanese Hezbollah and the implementation of a political plan which allows Israeli and Lebanese civilians to return to their homes to live in peace and security.
“That security will come through diplomacy – not escalation. There is no military solution here. Nor is there a military-only solution to the conflict in Gaza.
“This council must demand – again – an immediate, full and complete ceasefire in Gaza with the release of all the hostages.
“We need a political route to that agreement which provides a bridge to a better future. A credible and irreversible path towards a viable Palestinian state alongside a safe and secure State of Israel.
“This is the only way to provide security and justice for both Israelis and Palestinians.”