The UN Human Rights Office said Tuesday the reported execution of nine people accused of killing a Houthi leader in Yemen without due process is a violation of international law can amount to a war crime.

Marta Hurtado, a spokeswoman for the UN High Commissioner for Human Rights, said at a news conference in Geneva the office is "very concerned" that all the conflicting parties in Yemen are violating the basic principles of international law.

She cited the public execution on Sept. 18 by the Houthis of nine men, including one who reportedly was a minor when he was detained.

The nine were accused of having participated three years ago in the assassination of Saleh Ali Al-Samad, president of the group’s Supreme Political Council, who was killed in an airstrike.

The UN High Commissioner for Human Rights spokeswoman said that the defendants were sentenced to death “in a judicial process that violated their constitutional rights and did not comply with fair trial standards under international law.”

Hurtado said that international law establishes strict conditions for applying capital punishment, including compliance with fair trial and due process standards.

She said the execution of juvenile offenders is strictly prohibited under international law, regardless of the circumstances and nature of the crime committed.

“In the context of an armed conflict, carrying out the execution without affording judicial guarantees is also a violation of international humanitarian law and amounts to a war crime,” she added.

Yemen has been beset by violence and chaos since 2014, when Houthis overran much of the country, including the capital, Sanaa. The crisis escalated in 2015 when a Saudi-led coalition launched a devastating air campaign aimed at rolling back Houthi territorial gains.

According to the UN Office for the Coordination of Humanitarian Affairs, the conflict has claimed more than 233,000 lives./agencies