The coalition shut down Yemen's sea and air ports as well as borders on November 6 in response to a missile attack by the Iran-backed Huthi rebels near Riyadh.
After repeated appeals by UN officials were ignored, Guterres wrote to the Saudi ambassador today to ask for an end to the blockade which he said "is already reversing the impact of humanitarian efforts."
"The secretary-general is very much disappointed that we have not seen a lifting of the blockade," said UN spokesman Stephane Dujarric.
"This is a man-made crisis," continued the UN spokesman, adding that Guterres had called it a "stupid war."
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The United Nations has listed Yemen as the world's number one humanitarian crisis, with 17 million people in need of food, seven million of whom are at risk of famine.
Yemen is also battling one of the world's worst outbreaks of cholera, that has left nearly one million people ill and killed 2,200 people.
The direct appeal to Saudi Arabia's ambassador from the UN chief highlighted growing frustration and alarm over Yemen's humanitarian crisis and the coalition's refusal to open up access to aid.
In the letter, Guterres offered to send a UN team to Riyadh for talks on tightening up inspections at Hodeida port, once the aid shipments have resumed.
The coalition argues that ships docking at Hodeida port are used for arms smuggling to the Huthi rebels.
The joint appeal came from the World Health Organization, the UN children's agency UNICEF and the World Food Programme.
The coalition has partially eased some restrictions on ports controlled by the Saudi-backed Yemeni government, but the United Nations is insisting on access to Hodeida and Saleef ports.