US should maintain support to Saudis in Yemen: Mattis

The US Congress should not interfere with America's role in the war in Yemen, Defence Secretary Jim Mattis said, despite its support for Saudi-led coalition military operations in the war-torn country.

In a letter to congressional leaders this week, Mattis said that restricting US support to the campaign could lead to additional harm on the ground, because US targeting and intelligence are key to reducing the civil toll.

"New restrictions on this limited US military support could increase civilian casualties, jeopardise cooperation with our partners on counterterrorism, and reduce our influence with the Saudis - all of which would further exacerbate the situation and humanitarian crisis," Mattis wrote. 

On Thursday, Mattis told reporters accompanying him back to Washington after a visit to the Middle East that he sees the current path as helping push the Yemen crisis to a UN-brokered peace deal.

"We need to get this to a negotiated settlement and we believe the policy right now is correct, and that was the gist of my letter," Mattis said.

He wrote that withdrawing US support to the Saudi-led coalition would have knock-on effects resulting in deeper Iranian involvement in the war. 

It would enable "further ballistic missile strikes on Saudi Arabia and (threaten) vital shipping lanes, thereby raising the risk of a regional conflict," Mattis stated.

The comments came ahead of a planned Senate vote next week to decide on a measure that would curtail US involvement in Yemen's bloody civil war.

Some US lawmakers have long expressed concern about the conflict, which has seen high levels of civilian casualties and caused a humanitarian crisis.

A bipartisan group of senators including Bernie Sanders is pushing for the Senate vote, which could come just as Saudi Crown Prince Mohammed bin Salman is visiting Washington.

Since 2015, the Pentagon has provided "non-combat support" to Saudi Arabia, including intelligence sharing and air-to-air refuelling for its war planes.

Critics say Riyadh would be unable to conduct much of its campaign without US help.

More than 10,000 people have been killed since the Saudi-led coalition intervened to push back Houthi rebels from key cities, including the capital Sanaa, to reinstate the internationally recognised government of Abedrabbo Mansour Hadi.

On Thursday, the UN Security Council warned conditions in war-torn Yemen are worsening and having a "devastating" impact on civilians, with 22.2 million now in need of humanitarian assistance.

The council cited indiscriminate attacks on densely populated areas, with large numbers of civilian casualties and damage to civilian structures.