UN Secretary General Antonio Guterres has called for the 'immediate and unconditional release' of 11 UN staff arrested by Houthi authorities in Yemen.

The workers were detained by security forces in raids on the World Food Programme (WFP), children's charity Unicef, and the World Health Organization (WHO), news agencies and the UN said.

Sunday's raids took place in the capital, Sanaa, and port city of Hudaydah, UN Special Envoy for Yemen Hans Grundberg said.

Grundberg stated that the Houthis had already been holding 23 other UN workers arrested since 2021. Houthi authorities have not commented on these latest arrests.

In a statement on Sunday, Guterres said he 'strongly condemn[s] the arbitrary detentions of at least 11 UN personnel' by the Houthis. He also condemned the forced entry into WFP and other UN premises, as well as the seizure of property.

The reason behind the Houthis targeting UN workers is uncertain. However, the organization’s staff and aid workers have been crucial in providing support for ordinary Yemenis amid one of the world's worst humanitarian crises.

One of those previously arrested died while in detention earlier this year, as noted by Grundberg. The Houthis have also detained some 20 Yemeni employees of the US embassy over the past three years.

Despite efforts for dialogue, the arbitrary detention of UN staff, NGO workers, and civil society continues to be a challenge, severely hindering broader efforts to provide assistance and promote peace in Yemen, Grundberg remarked.

Earlier in the year, the UN had suspended all operations in Houthi-held areas following repeated detentions of its personnel.

The latest arrests come amid heightened tensions after an Israeli airstrike killed the Houthi prime minister and other high-ranking officials on Thursday. This marked a significant escalation in the conflict, which has seen the Houthis fire missiles at Israel in support of the Palestinian cause amidst ongoing hostilities.

The Iran-backed Houthis have maintained control over the capital and north-western regions of Yemen since toppling the internationally recognized government in 2015 during the civil war. The ongoing violence has resulted in over 150,000 fatalities and has wrought a catastrophic humanitarian disaster, displacing 4.8 million people and leaving around 19.5 million—half the population—in dire need of assistance.