According to the sources, the offices of the World Food Programme and the United Nations Children's Fund were raided on Sunday, and 11 employees were taken to an unknown location.
The motives behind the incident remain unclear. The Iran-backed Houthis, who have controlled Sanaa and large parts of northern Yemen for about a decade, have not yet commented on the matter.
The UN's Special Envoy for Yemen, Hans Grundberg, said he condemned "the new wave of arbitrary detentions of UN personnel", as well as the "forced entry into UN premises and seizure of UN property".
He reported that at least 11 UN employees had been detained.
Grundberg called on the militia to "release immediately and unconditionally all UN personnel, as well as staff from national and international [non-governmental organizations], civil society organisations, and diplomatic missions".
UN Secretary General António Guterres also condemned the detention of UN staff by the Houthis and the raids on aid organisation offices. In a statement, he demanded that those arrested be released immediately.
The Houthis have previously abducted UN staff and other aid workers in the war-torn country. Some of them have been imprisoned for more than three years. The Houthis accuse some UN staff of spying for the United States.
On Saturday, the Houthis announced the death of their Prime Minister, Ahmed al-Rahawi, and several ministers in an Israeli airstrike on Thursday. The Houthi government is not internationally recognised.
Houthi leader Abdel Malik al-Houthi declared that the militia would continue its fight against Israel despite the death of their prime minister. He stated that missile and drone attacks and the so-called "sea blockade" would persist.
Since the start of Israel's bombardment of Gaza in October 2023, the Houthis have primarily targeted commercial ships in the Red Sea with alleged links to Israel, as well as Israel itself.
Their stated goal is to support Palestinians in Gaza. Israel and its ally, the US, have repeatedly bombed targets in Yemen in response.
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