Yemen's Houthi rebels on Saturday said they executed nine people for their alleged involvement in the killing of a senior Houthi official in an airstrike by the Saudi-led coalition more than three years ago.

The public executions by firing squad were carried out in the rebel-held capital of Sanaa, according to the Iranian-backed Houthis who distributed photos apparently showing the executions. The executions took place despite repeated calls by rights groups and lawyers to stop the killings. They said the trial held in a rebel-controlled court where the nine were convicted and sentenced to death was flawed.

The nine were among more than 60 people the Houthis accused of involvement in the targeted killing of Saleh al-Samad in April 2018. Former President Donald Trump was also accused, according to court documents obtained by The Associated Press. Also accused were top Western, Israeli and Gulf officials.

The Houthis accused the nine of spying for the Saudi-led coalition.

Al-Samad, who held the post of president in the Houthi-backed political body, was killed in an airstrike by the Saudi-led coalition in the coastal city of Hodeida.

The nine, including a 17-year-old boy, were arrested months after al-Samad's killing. They had been forcefully disappeared for months in undisclosed places where they suffered inhuman treatment, according to Abdel-Majeed Sabra, a Yemeni lawyer representing one of the people executed.

Hundreds of people, mostly Houthis and their supporters, attended the executions, which were also broadcast on big screens early Saturday in Tahrir Square in the capital of Sanaa. The executions and their display cause outrage across the country, including Sanaa, where people refrain from criticising the rebels for fear of reprisals.

The nine wore sky blue prison garb with their hands bound behind their backs. Masked guards led them an open area and forced them to lie down on their stomachs. Another officer with a rifle shot them to death in their backs.