Saudi Arabia has asked the United Nations to move aid workers away from rebel-held areas in Yemen as the Riyadh-led coalition presses on with air strikes against insurgents, according to a letter seen by AFP Thursday.

The United Nations flatly rejected the request and reminded Saudi Arabia of its obligations to allow humanitarian access in Yemen, where coalition warplanes have been pounding Shiite Huthi rebels for nearly a year.

UN aid chief Stephen O'Brien said in a letter to Saudi Ambassador Abdallah Al-Mouallimi that relief organizations were "delivering life-saving assistance as per internationally recognized principles and will continue to do so."

Responding to O'Brien, the ambassador renewed the coalition's request that "humanitarian and relief organizations relocate from areas close to bases for military operations by Huthis and supporters" of ex-president Ali Abdullah Saleh.

"The coalition's request is consistent with its obligations under international humanitarian law, and, in no way, can be misinterpreted to indicate any hindrance to humanitarian access and the delivery of humanitarian assistance in Yemen," wrote Mouallimi on Monday.

The United Nations has had several disputes with Saudi Arabia over aid access in Yemen, where 80 percent of the population is facing dire food shortages.

O'Brien told Saudi Arabia that aid workers would continue to inform coalition authorities of their movements.

UN and international aid workers have passed on their coordinates to coalition military authorities to ensure they are not inadvertently targeted.

The Saudi-led coalition is backing Yemen's government in its war against Iranian-backed rebels who overran the capital Sanaa in September 2014.

More than 6,100 people have been killed in the conflict since March, about half of them civilians, according to UN estimates.

The United Nations is pushing for a ceasefire and political talks in Yemen.

A first round of UN-brokered negotiations in Switzerland in December did not yield any breakthroughs.

The UN Security Council will discuss the crisis in Yemen at a meeting on Wednesday.