The decision to pause all operations and programmes in northern Saada came after eight UN staff were detained by the Iran-backed Houthi rebels.

The UN has suspended its aid operations in Yemen's Saada region after eight more of its staff were detained by Houthi rebels.

In a statement, the UN said on Monday that the "extraordinary" decision to pause all operations and programmes in northern Saada province — a Houthi stronghold in the war-torn country — was due to the lack of necessary security conditions and guarantees.

The rebels in recent months have detained dozens of UN staff, as well as people associated with aid groups and the once-open US embassy in Sanaa, Yemen's capital.

Before the latest arrests, which happened late last month, the Iran-aligned Houthis had at least 24 UN workers in detention. None of them have been released to date.

"This pause is to give time to the de facto authorities and the United Nations to arrange the release of arbitrarily detained UN personnel and ensure that the necessary conditions are in place to deliver critical humanitarian support," UN deputy spokesperson Farhan Haq said.

Yemen is enduring one of the world’s worst humanitarian crises, with at least 19 million people in need of assistance and protection, according to the UN.

Haq could not say how many people would be affected by the pause in UN operations.

Seven UN agencies operate in Saada, including the World Food Program, the World Health Organization and UNICEF, along with several international aid organisations.

The Houthis have not commented on the UN's decision. The rebels have previously shown detained UN staffers on television channels and referred to them as collaborators with Israel and Western intelligence services.

Late last month, the UN suspended all travel into areas held by the Houthis after several of its staff were detained by the rebels.

The war in Yemen has killed more than 150,000 people, including fighters and civilians.

The Iranian-backed Houthis have been fighting Yemen's globally recognised government — which is supported by a Saudi-led coalition — since 2014, when they descended from their stronghold in Saada and took control of Sanaa and most of the north.

In January, the Houthis unilaterally freed 153 detainees as one of several overtures to ease tensions after the ceasefire in the Israel-Hamas war in Gaza. Such prisoner releases have been viewed as a means to jumpstart talks over permanently ending Yemen’s war.