The United Nations says 16 of its staff members have been detained in the Ethiopian capital, Addis Ababa.
A UN spokesperson said six others had been released.
He said the country’s Ministry of Foreign Affairs had been asked to free all of them immediately.
It is not yet clear why they were arrested.
Last month seven senior UN officials were expelled after being accused of meddling in Ethiopia’s affairs.
The UN has spoken out about human rights abuses and has accused the government of impeding the delivery of aid to millions of victims of a year- long conflict in northern Ethiopia.
There have been numerous accusations that Tigrayans have been arbitrarily arrested – something the government denies.
