The Saudi-led coalition operating in Yemen has denied killing civilians in an air strike in the northern province of Hajjah, saying it destroyed a bomb-making factory, not a water bottling plant.

Brigadier General Ahmed Asseri, the coalition spokesman, said on Sunday that Houthi rebels were using the location to train African migrants, whom they had forced to take up arms, and to make improvised explosive devices.

"We got very accurate information about this position and attacked it. It is not a bottling factory," he said.

Asseri accused the Houthis of using African migrants, stuck in Yemen after arriving by sea before the war in the hope of crossing the Saudi border and finding work in the oil producer, as cannon fodder in dangerous border operations.

Earlier on Sunday, resident Issa Ahmed told the Reuters news agency by phone that at least 36 civilians working in Abas in Hajjah were killed in the air raid.

"The process of recovering the bodies is finished now. The corpses of 36 workers, many of them burnt or in pieces, were pulled out after an air strike hit the plant this morning," he said.

The German news agency DPA also quoted medical officials as saying the target in Abas was a drinking water factory.

Killings

Meanwhile, in al-Mansour district of the port city of Aden, Colonel Abdelhakim Sanidi, the local director of security, was shot dead on Sunday outside his home by gunmen in a passing car, police officials said.

Later in the day, Hamdi Nasreddine Al-Shuteiri, a senior member of the Southern Resistance in the Khor Maksar district of Aden, was killed by unknown gunmen.

The deaths were the first killings sine the city was recaptured by fighters loyal to exiled President Abd-Rabbu Mansour Hadi in July.

Since then, a power vacuum has grown, with al-Qaeda group members moving into a main neighbourhood last week and unknown assailants blowing up the intelligence headquarters.

Also on Sunday, a bomb exploded near the vacated US embassy in the capital Sanaa.

The USs and other Western countries closed their missions in Yemen in February as the political feud between the Houthis and the Hadi government escalated.