The United Nations relief chief has warned that Yemen is facing a “humanitarian catastrophe”, urging warring sides to stop restricting aid access in the impoverished Arab country.

"The parties to the conflict have a duty of care in the conduct of military operations to protect all civilian persons and objects - including humanitarian and health care workers and facilities - against attack," Stephen O'Brien told the UN Security Council on Tuesday.

He said at least 7.6 million people are seriously “food insecure” in Yemen, noting that the war in the country has made over 1,170 schools and 600 health facilities unfit, as a result of which some 3.4 million children do not go to school.

UN aid chief Stephen O'Brien (Reuters photo)

The UN official asked all parties in Yemen to facilitate humanitarian access to all parts of the country, saying aid deliveries are very challenging across the country’s north due to Saudi airstrikes.

"UN agencies and NGO partners are delivering assistance under extraordinarily difficult and dangerous circumstances," said O'Brien, adding that last Sunday a Saudi airstrike hit a building 200 meters away from the Diplomatic Transit Facility, which accommodates UN and diplomatic personnel.

O’Brian also referred to Saudi Arabia’s recent warning to the UN and other aid agencies to withdraw staff from northern Yemen, saying this has impacted the planning of the humanitarian community.

Philippe Bolopion, a Human Rights Watch official, also said on Tuesday that "coalition members should be under no illusion that this warning absolves them of their obligation to distinguish between civilian and military objects, and to protect humanitarian personnel and facilities from attack" and said the Saudi warning could be considered a threat to aid workers.

He was referring to the Saudi-led coalition involved in the bloody war against Yemen.

On Monday, the World Food Program (WFP) also warned of famine in the city of Ta’izz as Saudi Arabia pressed ahead with its war campaign against Yemen.

Over 8,278 people, including children, have been killed since the Saudis started attacks on the poorest Arab country in March 2015. The strikes have also taken a heavy toll on the country’s facilities and infrastructure, destroying many hospitals, schools, and factories.