At least nine Yemeni staff of United Nations agencies have been detained by Yemen’s Houthi rebels under unclear circumstances, officials said on Friday, as the insurgents face growing financial pressure and air strikes from the US-led coalition. Others working for aid groups have also been detained.

The arrests come as the Houthis have been fighting a Saudi-led coalition since they seized Yemen’s capital nearly a decade ago and have targeted ships in the Red Sea corridor over the Israel-Hamas war in the Gaza Strip.

But as it has gained more international attention, the secretive group has also taken action against dissent domestically, including recently sentencing 44 people to death.

Talking to regional officials, he said, The Associated Press Those detained included staff from the U.N. human rights agency, its development program, the World Food Program and a man working for the office of its special envoy, officials said, speaking on condition of anonymity because they were not authorized to brief journalists. The wife of one of the detainees was also detained.

The United Nations declined to immediately comment.

The UN staff was also identified by the Mayoun Organization for Human Rights, which named other aid groups whose staff have been detained by the Houthis in four provinces – Amran, Hodeida, Saada and Sanaa. Those groups did not immediately acknowledge the detentions.

“We strongly condemn this dangerous escalation, which violates the privileges and immunities granted to UN staff under international law, and what we regard as repressive, authoritarian, blackmailing practices aimed at achieving political and economic gain,” the organisation said in a statement.

Activists, lawyers, and others also began writing an open online letter calling on the Houthis to immediately release those detained, because if they do not, it will “help further isolate the country from the world.”

Yemen’s Houthi rebels and their allied media organizations did not immediately acknowledge the detentions. However, the Iran-backed insurgents had planned weekly mass demonstrations after Friday afternoon prayers, when Houthi officials usually speak out on their actions.

It is not clear what the actual reason for the detention was. However, it came at a time when the Houthis are facing a shortage of sufficient currency to support the economy in the areas they occupy – something indicated by their move to introduce a new coin in the Yemeni currency rial. The Yemeni government in exile in Aden and other countries criticized the move as the Houthis have started resorting to counterfeit currency. The authorities in Aden have also demanded all banks to move their headquarters there.

“Internal tensions and conflicts could spiral out of control and lead Yemen to complete economic collapse,” warned Yemeni journalist Mohammed Ali Thamer in an analysis published by the Carnegie Endowment for International Peace.

Bloomberg reported separately on Thursday that the United States plans to step up economic pressure on the Houthis by blocking their revenue sources, including a $1.5 billion Saudi Arabian plan to pay salaries for government workers in rebel-held territory.

The war in Yemen has killed more than 150,000 people, including combatants and civilians, and has become one of the world’s worst humanitarian disasters, with tens of thousands more dead. The Houthis’ attacks on shipping have helped divert attention from domestic problems and the deadlocked war. But they have faced mounting casualties and damage from US-led air strikes targeting the group over the past few months.

Thousands of people have been imprisoned by the Houthis during the war. An AP investigation found some detainees were burned with acid, hung by their wrists for weeks or beaten with sticks. Meanwhile, the Houthis have hired child soldiers and indiscriminately planted landmines in the conflict.

The Houthis have previously detained four other U.N. staff — two in 2021 and two in 2023 — who are still being held by the militia group. In 2023, the U.N. human rights agency described those detentions as “extremely worrying as they reflect a total disregard for the rule of law.”

The Houthis are members of the minority Shia Zaydi sect of Islam that ruled northern Yemen for 1,000 years until 1962.