Yemeni Prime Minister Shaya al-Zindani said more than 70 UN staff members and dozens of humanitarian workers remain in Houthi custody.
United Nations High Commissioner for Human Rights Volker Türk has called for an urgent investigation into the death of a UN staff member in Houthi custody.
Mohammad el Shami, who worked at the UN Human Rights Office in Yemen, died after being "arbitrarily held" by the Houthis since 6 June 2024, according to a statement from the high commissioner's office on Saturday.
Shami's family said he had died more than a month ago but that they had only recently been informed, per the statement.
Türk called his death a "heartbreaking loss" for the UN as he expressed his condolences to Shami's family and loved ones.
He added that the family had not received "any explanation of the cause or circumstances of his death" and demanded transparency from Houthi authorities.
"This requires disclosure of all relevant medical and detention records, preservation of evidence and independent scrutiny of any stated cause of death. There must be accountability for wrongdoing," Türk said.
“I am also gravely concerned for the safety and wellbeing of the other UN personnel who remain detained, including seven colleagues from my Office, as well as detained humanitarian and civil society workers. I appeal again for their immediate and unconditional release," he added.
Yemeni Prime Minister Shaya al-Zindani condemned the death and said the Houthis "bear full responsibility."
He added that more than 70 UN staff members and dozens of humanitarian workers remain in Houthi custody.
In June 2024, the Houthis said a number of people they accused of belonging to a US-Israeli "spy network" had been arrested in Yemen.
The Iran-aligned Houthi rebels have launched a renewed offensive in Yemen in recent months, seizing territory as fighting with the country's internationally recognised government has intensified.
Neighbouring Saudi Arabia has carried out strikes against the group in a bid to hamper its advance, prompting the Houthis to launch missiles and drones at Saudi cities and shipping. The group also declared a naval blockade of Saudi Arabia in July.
A Houthi strike on Riyadh's King Khalid International airport last month left 13 people dead and more than 300 injured, according to Saudi Arabia's General Authority of Civil Aviation.