The resolution, submitted by Britain, was the subject of tough negotiations among the 15 council members, and was amended several times before the vote on Friday.
The resolution also endorsed the results of UN-brokered peace talks in Sweden last week, when Yemen’s warring parties agreed to a ceasefire that took effect on Tuesday.
A withdrawal of fighters in Hodeidah, a key gateway for aid and food imports in the impoverished nation, was a part of the truce.
The ceasefire between Saudi-backed government forces and Houthi rebels is seen as the best chance yet of ending four years of Yemen’s devastating conflict.
The agreement also included a planned prisoner swap involving some 15,000 detainees.
What the UN resolution says
The resolution authorises the UN to “establish and deploy, for an initial period of 30 days … an advance team to begin monitoring” the ceasefire, under the leadership of retired Dutch general Patrick Cammaert.
The UN team, led by Cammaert, is due to arrive in Yemen shortly, said a UN spokesman, adding that the personnel will not be uniformed or armed.
The resolution also authorises UN Secretary General Antonio Guterres to “submit proposals as soon as possible before December 31, 2018 on how the United Nations will fully support the Stockholm Agreement as requested by the parties”.
French ambassador Francois Delattre said the unanimous vote sent a “strong signal of the council’s unity and engagement” on Yemen, and that it had put its weight behind the UN-brokered talks.
Diplomats said the UN observer mission could consist of 30 to 40 people, tasked with ensuring the withdrawal of the warring parties from Hodeidah and the safe passage of humanitarian aid.
The observers will head up monitoring teams made up of government and rebel representatives, under the auspices of a Redeployment Coordination Committee headed by Cammaert.
‘World’s worst humanitarian crisis’
Yemen, the Arab world’s poorest country, has been devastated by a multi-sided conflict involving local, regional and international actors.
The conflict began with the 2014 takeover of the capital, Sanaa, by the Houthis, who toppled President Abd-Rabbu Mansour Hadi’s government.
A Saudi-UAE-led coalition allied with Yemen’s internationally recognised government has been fighting the Houthis since 2015.
Since then, more than 60,000 people have been killed in the fighting, according to estimates by rights groups, and as many as 85,000 children may have starved to death.
On December 8, the UN said that as many as 20 million people in Yemen were “food insecure,” calling the situation the “world’s worst humanitarian crisis”.
Louis Charbonneau, the UN director for Human Rights Watch, said the resolution “sends an important message to the suffering people of Yemen that they haven’t been forgotten”.