The United Nations has suspended humanitarian operations in northern Saada after rebels detained eight more U.N. staffers, during one of the world's worst humanitarian crises.

The United Nations said on Tuesday that one of its staff members had died in detention in northern Yemen, where the U.N. has repeatedly called for the Houthi movement to free detained U.N. employees.

A World Food Programme (WFP) worker has died while in detention in Houthi-controlled northern Yemen, according to the UN agency. The WFP said the man was one of seven Yemeni staff "arbitrarily detained" by local authorities since 23 January.