The U.N. food agency says one of its staffers detained last month by Houthi rebels in Yemen has died in prison.

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. It is unclear when or how he died.

The United Nations World Food Programme 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.