Yemen's Houthis raided United Nations offices in the Yemeni capital Sanaa on Sunday and detained at least 11 UN personnel, the body said.
UN Secretary-General Antonio Guterres said the Houthis forcibly entered World Food Programme premises, seized UN property and attempted to enter other UN offices in the capital.
The raid followed an Israeli strike on Sanaa on Thursday that killed the prime minister of Yemen's Houthi-run government and several other ministers.
UN Special Envoy for Yemen Hans Grundberg said in a separate statement that the 11 staff were detained in both Sanaa and the port city of Hodeidah.
UNICEF, the UN Development Programme and the office of the U.N. High Commissioner for Refugees are among other U.N. agencies with offices in one or both of the two cities.
Grundberg said the detentions were in addition to 23 other UN staff previously detained, some since 2021, and one who died in detention this year.

Afghanistan says Pakistan strikes kill and injure dozens
Police officer killed, dozens injured in bomb explosions in Ukraine's Lviv
Trump pivots to new 15% global tariff after Supreme Court setback
Hong Kong plans to buy homes devastated in deadly high-rise fire
US Supreme Court strikes down Trump's global tariffs
