Saleh al-Sammad was head of the Huthis' supreme political council and his death three years ago was seen as a major blow to the Iran-backed rebels who control Sanaa.

The pro-rebel Saba news agency said the nine were shot by a firing squad at a square in the Yemen capital.

They were among 17 people convicted of involvement in his killing by a Huthi court.

Seven other people -- including Saudi Crown Prince Mohammed bin Salman and former US president Donald Trump -- were tried in absentia by the court and also sentenced to death.

Sammad was killed in April 2018 alongside six other people in an air strike in the western Yemeni province of Hodeida.

"The general prosecution has carried out the death sentence against nine people involved in the murder" of Sammad, Saba reported.

"They were shot to death in Tahrir Square... in the presence of senior Huthi leaders and Sanaa residents," the agency added.

Saudi Arabia said later that it carried out the air strike.

"The heroes of the Royal Air Force were able to successfully target the leader of the Huthi militia Saleh al-Sammad," Saudi Arabia's ambassador to the United States, Prince Khaled bin Salman, tweeted at the time.

Prince Khaled said the strike was overseen by his brother the Saudi crown prince, after Sammad threatened a wave of missile strikes against Saudi Arabia.

The Huthis are battling the Saudi-backed Yemeni government -- and a military coalition spearheaded by Riyadh -- for control of the impoverished country.

The conflict began in 2014 when the Huthis seized Sanaa, prompting the Saudi-led coalition to intervene the following year.

Since then, tens of thousands have been killed and millions pushed to the brink of famine in what the United Nations calls the world's worst humanitarian crisis.

Sammad was the most senior Huthi leader to have been killed since the Saudi-led coalition intervened in the country.

The Huthis -- who had vowed to avenge his death -- have regularly launched ballistic missiles into Saudi Arabia.

In August this year they escalated cross-border attacks by also using drones.