The U.N. Security Council is expressing "grave concern" that agreements reached four months ago by the warring parties in Yemen have not been carried out and is calling for their implementation "without delay."

In a statement Wednesday, the council reiterates its endorsement of the Dec. 13 cease-fire agreement between Yemen's government and Houthi Shiite rebels that calls for the "phased but rapid mutual withdrawals" of fighters from the main port in Hodeida, two other ports in the province and Hodeida city.

Council members welcomed the rival parties' agreement on the military plan for the initial redeployment of forces from Hodeida, and urged them to swiftly agree on plans for the second phase of withdrawals.

The council notes "with concern continued violence that risks undermining the cease-fire in Hodeida."