Saudi Arabia's Defense Ministry says Houthi rebels in Yemen have fired a mortar round at a border post, killing three Saudi officers and wounding two others.

An unnamed military official is quoted in a Defense Ministry statement Saturday as saying that the incident took place the day before in the Saudi border province of Najran.

The Saudi Defense Ministry says its forces responded with gunfire. It says that since its campaign against the Houthis began last month, 500 Houthi fighters have been killed in clashes along the border.

Earlier this month, three Saudi border guards were killed in separate clashes with the Houthis.

A Saudi-led coalition is targeting the Houthis from the air, and has imposed a virtual air and sea blockade on Yemen to prevent the rebels from rearming.