Saudi Arabia has cautioned the United Nations and international aid groups to protect staff by evacuating them from the areas controlled by Houthi militants, Reuters cited a letter as saying on Thursday.
Saudi Arabia is leading a coalition of nine Arab countries that began a military campaign in March to prevent Iran-allied Houthi militants from taking complete control of Yemen.
According to the letter the intention was to "protect the international organizations and their employees," presumably from coalition air strikes.
The Saudi ambassador to the United Nations in New York, Abdallah Al-Mouallimi, told Reuters that Riyadh sent the letter because, "We're just concerned for the safety of the UN staff and their humanitarian agencies.
"We want them to go away from areas that are obvious targets," he said.
UN aid officer Stephen O'Brien was aware of the letter and said the deliverance of humanitarian aid would continue across Yemen on the basis of need.
He cautioned Saudi Arabia to follow international humanitarian law on the provision of aid.
On Monday, the Saudi mission to the United Nations said Riyadh would "do its utmost to continue to facilitate and support" humanitarian aid work in Yemen, while repeatedly calling for UN and international aid workers to evacuate areas near to Houthi strongholds.
"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," it said.
Diplomats said the UN Security Council is planning to discuss humanitarian conditions in Yemen on Tuesday at the request of Russia.
Houthi militants together with their Iranian allies, also aligned with forces loyal to ousted Yemen President Ali Abdullah Saleh, accused the Saudi coalition of war crimes.
Since the coalition began its military intervention in March, nearly 6,000 people - mostly civilians - have been killed.
Last month UN sanctions monitors said that the Saudi-led coalition had conducted air strikes killing civilians and that some of the strikes could be crimes against humanity.