US President Joe Biden has declared a halt to US support for a Saudi Arabia-led military campaign in Yemen, demanding that the more than six-year war, widely seen as a proxy conflict between Saudi Arabia and Iran, “has to end”.

Mr Biden also named veteran diplomat Timothy Lenderking as the US special envoy for Yemen in a bid to step up American diplomacy “to end the war in Yemen, a war which has created humanitarian and strategic catastrophe”.

The United Nations describes Yemen as the world’s biggest humanitarian crisis, with 80 per cent of its people in need and millions on the verge of a large-scale famine.

“This war has to end,” the Democratic president said during a visit to the US State Department in Washington on Thursday (local time). “And to underscore our commitment, we’re ending all American support for offensive operations in the war in Yemen, including relevant arms sales.”

The move is a reversal of a policy of both the Democratic Obama and Republican Trump administrations. Biden was vice-president in the Obama administration.

“At the same time,” he said on Thursday, “Saudi Arabia faces missile attacks, UAV (drone) strikes and other threats from Iranian-supplied forces in multiple countries. We’re going to continue to support and help Saudi Arabia defend its sovereignty and its territorial integrity and its people.”

Saudi Arabia welcomed Mr Biden’s remarks, particularly his commitment to the country’s defence and addressing threats against it, according to the country’s state news agency.

The Saudi-led military coalition intervened in Yemen in 2015, backing government forces fighting the Iran-aligned Houthis. UN officials are trying to revive peace talks to end the war.

Under the Trump administration, policy on Yemen was secondary to a so-called “maximum pressure” sanctions campaign against Iran in a bid to force Tehran back into talks over its nuclear and missile programs and activities in the Middle East.

Former president Donald Trump was also focused on maintaining close ties with Saudi Arabia’s effective ruler, Crown Prince Mohammed bin Salman, which included US arms sales.

The ending of US support for the offensive would not affect American operations against the Yemen-based al-Qaeda in the Arabian Peninsula, national security adviser Jake Sullivan said.

-AAP