The United Nations says it hopes Yemen's warring parties will immediately carry out an agreement to pull their forces out of the key port of Hodeida and two smaller ports, as well as a U.N. facility holding enough grain to feed 3.7 million people for a month.

Hodeida handles about 70 percent of Yemen's imports and U.N. deputy spokesman Farhan Haq told reporters Monday that implementation is key there and at the two other ports and the Red Sea Mills where the U.N. humanitarian chief has implored Houthi Shiite rebels to facilitate access.

Yemen's government has been battling the rebels since 2014. The fighting has killed thousands of civilians and created the world's worst humanitarian crisis.

The two sides reached agreement Sunday on the first phase of a mutual pullout.