The UN will have to prove its relevance as wars in the Middle East, Ukraine and Sudan rage on

The mood is sombre and uncertain as 140 world leaders converge on New York for the UN's annual meeting.

Since their last gathering, war has erupted in the Middle East and threatens to widen, the conflict in Sudan has deepened and the Ukraine one has spread and worsened with no end in sight.

The leader of the free world is bowing from the world stage, too old and frail to run for a second term in office.

As Joe Biden's presidency enters its twilight hours, America's role in the world is once again in question.

There is a 50/50 chance of Mr Biden being replaced by a man viscerally suspicious of the multilateral world order.

A second Donald Trump presidency threatens an American retreat from the world at a crucial juncture jeopardising US support for NATO, Ukraine and the UN.

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Leaders will posture and grandstand as they do every year in the UN's hallowed halls.

But the UN General Assembly is also a chance for world leaders to meet, thrash out differences and forge consensus to solve the world's challenges.

Allies, rivals and sworn enemies will for a few days be in the same place. Their gathering brings gridlock to the island of Manhattan but also the possibility of progress.

Iran's president will walk the same corridors as Israel's prime minister.

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Ukraine's leader Volodymyr Zelenskyy will be there at the same time as Vladimir Putin's right-hand man on the world stage, Russian foreign minister Sergei Lavrov. There is always the hope of reconciliation.

But the outlook this year is gloomy.

UN-convened diplomacy has failed utterly to reverse Russian aggression in Ukraine just as Western sanctions failed to deter it.

Some member countries are openly supporting Moscow's continuing violation of the UN's founding principles.

Others are turning a blind eye or making a profit from the war.

Likewise with Sudan, with different countries choosing sides and failing to end its devastating conflict.

Overshadowing the week most of all will be the war in Gaza and the fear the conflict in the Middle East is entering a new phase.

The prelude to this meeting has been an extraordinary week of assassinations and mysterious electronic device attacks in Lebanon and an intensifying exchange of fire between Hezbollah and Israel.

As leaders gather in New York there remains the very real danger of a regional Middle Eastern conflagration erupting.

Whatever the lofty rhetoric and aspirations we will hear this week, the UN will have its work cut out simply proving its relevance in a world that is dangerously unravelling.