The United Nations on Friday suspended all travel into areas held by Yemen’s Houthi rebels after more of their staff were detained by the rebels.

The UN said that the Houthis who control northern Yemen had detained an unspecified number of UN personnel, and it was suspending movement in Houthi-led areas.

All official movement of U.N. staff into or within Houth-held areas had been suspended to protect the safety of staff. The U.N. was actively engaging with senior Houthi representatives to demand the immediate and unconditional release of all its detained personnel and partners.

The United Nations (UN) says it has suspended all movement in Houthi-held areas of Yemen after a number of UN personnel were detained by the armed group in the capital, Sanaa. The UN said that it was actively engaging with senior Houthi officials to try to secure the release of all its detained employees.

The UN said on Friday it was suspending “all official movements” in Houthi-controlled parts of Yemen after the rebel group detained a number of people employed by the world body. The office of the resident UN co-ordinator for Yemen called for the “immediate and unconditional” release of all its detained staff held in the country.