Air strikes by Saudi-led forces hit oil facilities in Yemen on Thursday, killing at least nine people, workers and medics said, and four Yemeni government soldiers died in a suspected militant attack.

The air attack on a Red Sea facility at Ras Isa port, used to load tanker trucks with refined products for domestic distribution, wounded at least 30 other people, medical sources said.

"The bodies were either burned or mutilated, most of the wounded suffering burns from the burning fuel," one source told Reuters in a text message.

Photos showed fire trucks trying to put out flames rising from fuel trucks as black smoke covered the area.

Ras Isa is Yemen's main oil export terminal but no shipments have been leaving since the Saudi-led coalition of Arab states launched a military campaign in March last year to shore up President Abd-Rabbu Mansour Hadi against his Iran-allied Houthi enemies.

Oil workers said the oil export facilities in the area and a nearby sugar refinery were not affected by Thursday's attack.

The United Nations says nearly 6,000 people have been killed in fighting which began after the Houthis advanced on the southern port city of Aden, where Hadi had been based. Hundreds of thousands of people have been displaced by the fighting.

In eastern Yemen, four Yemeni government soldiers were killed and four wounded in a bomb attack on their vehicle near a border post between Yemen and Saudi Arabia, a government official said.

The official said al Qaeda militants, who are known to operate in the area, were suspected of carrying out the attack at al Wadia.