Riyadh (AFP) - Fighting along Saudi Arabia's border with Yemen has killed a soldier from the kingdom, the Saudi-led coalition spokesman said on Saturday.

The soldier is the seventh to die since coalition aircraft on March 26 began air strikes in Yemen to stop a southern advance by Iran-backed Huthi rebels.

Brigadier General Ahmed al-Assiri told reporters there was continuous fighting from Friday afternoon until late that night along the frontier in the southwestern Saudi region of Najran.

"One of our Saudi soldiers was killed," Assiri said, adding that the coalition has carried out more than 2,000 aerial sorties during the three-week campaign.

Western diplomats have said Saudi warplanes conducted most of the coalition strikes.

Three other Saudi soldiers and three members of the kingdom's Border Guard force have also been killed in clashes along the southwestern frontier.

Saudi Arabia has reinforced the border with artillery, tanks and hilltop lookout posts to block the incursion of any Huthis, whose traditional stronghold is just over the border in northern Yemen.

The rebels swept into the capital Sanaa last September from their highland bases and then advanced south on the port of Aden, forcing President Abedrabbo Mansour Hadi to flee to Riyadh and the coalition to take action.

The rebels, allied with army units loyal to former president Ali Abdullah Saleh, are fighting Hadi loyalists on the ground.

The United Nations says hundreds of civilians have died in the fighting which has left food, water and other essentials in short supply.

Aid has only trickled into Yemen, largely because of restrictions imposed by the coalition on its airspace and ports.

Assiri said two cargo loads of relief supplies and food donated by Qatar and the United Arab Emirates have reached Aden and Yemen's Red Sea city of Hodeida, via Djibouti in the Horn of Africa.

"Other cargos will follow in the coming days," he said. "We will be speaking about a sea bridge to get aid to the Yemeni people."

Story continues

He reiterated that the movement of ships or aircraft must be coordinated with the coalition.

On Friday a Kenyan aircraft tried to reach Sanaa without such clearance, Assiri said.

"We forced it to land" on the Saudi side of the border, where initial investigation revealed that the rebels "are issuing false clearance" to aircraft, the spokesman said.

Assiri did not specify if the Kenyan plane carried relief materials.

The aid group Doctors Without Borders (MSF) separately said "more than 70 tonnes of medical material" arrived by plane in Sanaa on Saturday.