The war in the Middle East has effectively closed the Strait of Hormuz, while fuel supply disruptions are sending freight rates soaring.

UN aid chief Tom Fletcher warned that the escalating war and the impact on the strait was having "a direct impact on our humanitarian supplies, including going to areas of key need in sub-Saharan Africa".

"I'm worried that further escalation will damage other supply routes," he told reporters in Geneva, warning that this was happening as the war "drives up the prices and... drives more people into greater need".

"So we're appealing to all the parties to try and secure those routes, including the Strait of Hormuz for our humanitarian traffic... so we can reach anyone, anywhere, on the basis of greatest need, and not on the basis of politics."

"We're living through a moment right now of grave peril," Fletcher said.

"We're seeing these crises escalate rapidly and increasingly collide in dangerous ways," he said, calling for "calmer heads to prevail".

The last two weeks of fighting are further confirmation that "we're living in a time of brutality, impunity and indifference", he said, cautioning that "the rules-based scaffolding meant to restrain the worst excesses of war is cracking".

"Human ingenuity is being applied to find ever more sinister ways to kill at scale, while civilians are subjected to ever more abject violence."