Yemeni security officials say Shiite rebels and their opponents are battling across several provinces hours after the start of a five-day humanitarian pause in the Saudi-led air campaign.

The officials, speaking on condition of anonymity because they were not authorized to brief reporters, say coalition planes carried out flyovers Monday but did not drop munitions.

The rebels, known as Houthis, said in a statement that they fired missiles across the border at a Saudi military position in the kingdom's Jazan region.

Security officials say the Houthis are battling their opponents north of the southern port city of Aden, and officials and witnesses say there are sporadic clashes in Yemen's central Marib province.

Ground fighting erupted in multiple provinces within minutes of the start of the unilateral cease-fire late Sunday.