A mortar shell killed a Border Guard soldier patrolling the frontier with Yemen on Thursday, the Interior Ministry said, bringing to 11 the number of Saudi casualties during its five-week campaign against Yemen's Houthi rebels.

Private Gharbi Rajah Al-Hassan Al-Mujaishi was patrolling on Thursday morning in the Hareth sector in Jazan province when he was killed, the Ministry said in a statement carried by the SPA. He was delivering supplies in Jazan.

Meanwhile, the Saudi-led coalition pressed on with airstrikes Thursday against Shiite rebels in south Yemen where fierce clashes raged between the insurgents and southern pro-government fighters, local sources said.

Warplanes hit Houthi rebel positions in the main southern city of Aden, in the districts of Khor Maksar and Dar Saad, helping pro-government forces to retake positions, sources among the southern fighters said.

Eight people were killed in overnight clashes in Aden, including five pro-government fighters and three civilians, according to the city's health chief Al-Khader Laswar.

He said 44 others were wounded.