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 reported.

Sunday's raids occurred in the capital, Sanaa, and the port city of Hudaydah, according to UN Special Envoy for Yemen Hans Grundberg.

This latest incident adds to a troubling history, as the Houthis have already been holding 23 other UN employees arrested since 2021.

Houthi authorities have not provided any comments regarding these recent arrests.

In a statement on Sunday, Guterres strongly condemned the arbitrary detentions, as well as the forced entry into WFP and other UN premises, which included property seizures.

The motives behind the Houthis' actions remain unclear, especially considering that UN staff have been providing vital humanitarian aid in Yemen, which has faced one of the world's worst humanitarian crises for several years.

Notably, one staff member previously arrested died in detention earlier this year.

Moreover, the Houthis have detained approximately 20 Yemeni employees working at the US embassy over the last three years.

Grundberg emphasized that despite ongoing dialogues and assurances over the past year, the arbitrary detentions have persisted. He stated, 'These actions severely hinder broader efforts to deliver assistance and advance peace in Yemen.'

Earlier this year, the UN had to suspend all movements in Houthi-controlled areas following similar detentions.

The recent arrests come amid heightened tensions following an Israeli attack that resulted in the death of the Houthi prime minister and other top officials.

This attack marks a significant escalation in Israel's retaliation against the Houthis, who have been launching missile attacks against Israel since November 2023 in solidarity with Palestinians in Gaza.

Since ousting the internationally recognized government in 2015 amidst civil war, the Iran-backed Houthis have maintained control of the capital and northwest Yemen.

The ongoing conflict has resulted in over 150,000 fatalities, displacing 4.8 million people, while 19.5 million—half of Yemen's population—are in desperate need of aid.