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Saudi Arabia has warned the United Nations and other aid agencies to move aid workers away from rebel-held areas in Yemen, where the Saudi-led coalition is , according to a letter revealed on Thursday.

According to media reports, the Saudi mission in Geneva sent an initial letter to the UN's Office for the Coordination of Humanitarian Affairs (OCHA) on 5 February.

The letter asked the UN agency to "notify all the working in Yemen" to relocate their staff away from "in order for the Coalition forces to guarantee the safety and security of the international organisations."

A similar letter marked urgent was sent out by the Saudi embassy in London.

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

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

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.

Responding to O'Brien, the Saudi ambassador for relief organisations to leave areas under rebel control.

"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 , 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 revelations come as the Saudi-led coalition carried out intense airstrikes in the in the early hours of Friday morning.

Eyewitnesses told °®Âþµº that a huge explosion rocked the capital's al-Sabeen district after a coalition air raid, which was followed by a number of other strikes in the neighbouring areas.

The Saudi-led coalition is backing the government of President Abd Rabbo Manour Hadi in its war against Houthi 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.

Agencies contributed to this report