Three Saudi officers have been killed and two others wounded after Houthi fighters in Yemen fired a mortar round at a Saudi border post, according to Saudi Arabia's defence ministry.

A statement from the ministry on Saturday said the incident took place the previous day in the Saudi border province of Najran.

The Saudi forces responded with gunfire, the statement said.

The ministry statement also said that since its campaign against the Houthis began last month, 500 Houthi fighters had been killed in clashes along the border.

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

Al Jazeera's Mohamed Vall, reporting on Sunday from Jizan on the Yemen border, said the Saudi deaths could have an impact on the campaign in Yemen.