Three people were killed at a Yemen border crossing when a Saudi immigration worker opened fire, killing a colleague and police officer before being shot himself, Saudi authorities said Sunday.

The 34-year-old employee of the Wadia crossing shot two of his colleagues at the frontier post on Saturday night, after they accused him of missing shifts, the Najran province administration said via Twitter.

One died instantly while another was injured and hospitalised.

The gunman went on to kill a police officer before being shot dead as he tried to flee the scene.

The Najran authority made no link between the attack and the war in Yemen, where Saudi Arabia is leading a military coalition battling Iran-backed Houthi rebels.

In June, Saudi authorities said they had killed fighters heading to the Saudi border from Yemen.

Saudi Arabia said the fighters belong to Lebanon's Hezbollah, which like Yemen's Houthis has links to Iran. Hezbollah has denied the charge.

Nearly 10,000 people have been killed in the war between Yemen's government and Houthi insurgents, including 2,200 children.