The Moroccan military announced on Monday that one of its F-16 fighter jets participating in the Saudi-led coalition against the Houthi rebels in Yemen has been missing since early Sunday evening.

A statement from the armed forces on state news agency MAP said that the pilot of a second jet accompanying the missing aircraft was unable to see if his counterpart had ejected, and that an investigation was underway. The plane was last seen at 6 p.m. local time (1500 UTC/GMT) on Sunday.

The Houthis also accepted a ceasefire proposal from Saudi Arabia on Sunday, with a five-day humanitarian truce set to begin on Tuesday at 11 p.m. amid international concerns that without diplomacy the situation in Yemen could rapidly deteriorate. Despite the call for a cessation of hostilities, the coalition continued to pound rebel targets over the weekend.

While not specifically referring to the Saudi offer, the rebels expressed "readiness to deal positively with any efforts, calls, or measures that would help end the suffering."

The United Nations has expressed great worry over the civilian death toll from the conflict, estimating that 1,400 people have died since the Houthis overran the capital Sanaa in March. There have also been deep concerns about the ability to deliver humanitarian aid as the Saudi coalition bombarded the airports in Sanaa and Yemen's second city of Aden.

The long-festering unrest of the Shiite Houthi rebels in majority-Sunni Yemen boiled over in April, when the insurgents overran the capital and forced internationally recognized President Abed Rabbo Mansour Hadi to flee to sympathetic Riyadh.

es/msh (AFP, dpa)