UN Secretary-General Antonio Guterres called Sunday for a renewed push to end the "stupid war" in Yemen, saying he hoped the Trump administration could pressure Saudi Arabia to ease the humanitarian crisis there.

"I believe this is a stupid war. I think this war is against the interests of Saudi Arabia and the Emirates... (and) of the people of Yemen," he said on CNN, employing unusually blunt language for the top UN diplomat.

"What we need is a political solution."

US President Donald Trump on Wednesday took the rare step of publicly demanding that ally Saudi Arabia immediately allow vital humanitarian supplies to reach Yemen, scene of what the UN calls the world's worst humanitarian crisis, with millions at risk of starvation.

Trump, while not asking for an end to Saudi-led bombing of Yemen, said in a statement that his aides would ask the Saudis to "completely allow food, fuel, water and medicine to reach the Yemeni people, who desperately need it."

Guterres said conditions in Yemen had improved somewhat, adding, "I hope that President Trump has put a lot of pressure recently... A lot of humanitarian aid is already going in."

He said he hoped a Saudi blockade of Yemen's ports, imposed after a Huthi missile was intercepted near Riyadh last month, would be lifted.

Saudi Arabia and its allies have launched a campaign to oust Huthi rebels who control the capital Sanaa and who have links to Riyadh's arch-foe Iran.

As the war drags on, seven million people are believed to be on the brink of famine and a cholera outbreak has caused more than 2,000 deaths.

"This war is causing, in my opinion, terrible suffering to the Yemeni people," while also harming Saudi Arabia and the Emirates, Guterres told CNN.

"It's in the interests of everybody to stop this war."