In another air raid on the capital Sanaa, residents said four civilians were killed when a bomb hit their house near a military base in the south of the city.
The attacks were the latest in an air campaign launched in March an alliance made up mainly of Gulf Arab states in support of the exiled government in its fight against Houthi forces allied to Iran.
“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,” resident Issa Ahmed told Reuters by phone from the site in Hajjah.
A Saudi military spokesman did not immediately respond to Reuters requests for comment on the reported attacks.
Human rights group Amnesty International said in a report this month that the campaign had left a “bloody trail of civilian death” which could amount to war crimes.
Air strikes killed 65 people in the frontline city of Taiz last Friday, most of them civilians, and the bombing of a milk factory in Western Yemen in July killed 65 people including 10 children.
More than 4,300 people have been killed in five months of war in Yemen while disease and suffering in the already impoverished country have spread.
Militias and army units loyal to President Abd-Rabbu Mansour Hadi, currently taking refuge in Saudi Arabia, have made significant gains toward the Houthi-controled capital in the last two months but the group remains ensconced in Yemen’s north and casualties mount in nationwide combat every day.
Also on Sunday, a bomb exploded near the vacated U.S. Embassy in Sanaa and unknown gunmen shot and killed a senior security official in the southern port city of Aden.
There were no immediate claims of responsibility, but Al Qaeda in the Arabian Peninsula – the deadliest branch of the global militant organization – has been attacking the Yemeni state and plotting against Western targets for years.
A powerful bomb detonated in front of a gate on the wall surrounding the embassy around midnight on Sunday but claimed no casualties, residents and officials said.
The United States and other Western countries closed their missions in Yemen in February as the political feud between the Houthis and the Hadi government led to war.
The Houthi-run state news agency Saba quoted a security official calling it a “terrorist and criminal act”.
In Aden, the local director of security, Colonel Abdul Hakim Snaidi, was shot dead outside his home by gunmen in a passing car, a security official said.
His death is the first such killing of a senior security official since the city was recaptured by pro-Hadi militiamen in July. Since then, a power vacuum has grown, with Al Qaeda militants moving into a main neighborhood last week and unknown assailants blowing up the intelligence headquarters.