Sixteen UN national staff have been detained in Ethiopia, while six others have been released, according to a spokesman on Tuesday.
"We are, of course, actively working with the Government of Ethiopia to secure their immediate release," Stephane Dujarric, spokesman for UN Secretary-General, Antonio Guterres, said at a news conference.
"No explanation was given to the international body why the staffers were detained," said Dujarric.
Ethiopian authorities have yet to comment.
In late September, Addis Ababa ordered seven UN officials to leave the country, accusing the staffers from different UN organizations of "meddling in the internal affairs" of the nation. They had been declared "persona non grata."
Guterres "was shocked" at the expulsion and said, then, that all UN humanitarian operations are guided by the core principles of humanity, impartiality, neutrality, and independence.
Ethiopia declared a state of emergency last week as the Tigray People's Liberation Front (TPLF) made military gains in the Amhara region, adjacent to the Tigray region.
The TPLF said it had controlled the strategic cities of Disi and Kombolcha in the northern state of Amhara.
Millions have been internally displaced due to the Tigray conflict, according to the UN, which warned of a humanitarian catastrophe.
Prime Minister, Abiy Ahmed, sent troops to Tigray last November, in response to attacks on army camps by the TPLF.