"We are, of course, actively working with the government of Ethiopia to secure their immediate release," U.N. spokesperson Stephane Dujarric told reporters in New York.
He declined to answer a question on the ethnicity of those detained, saying: "These are United Nations staff members, they're Ethiopians ... and we would like to see them released, whatever ethnicity is listed on their identity cards."
The state-appointed Ethiopian Human Rights Commission said on Sunday it had received many reports of arrests of Tigrayans in the capital, including elders and mothers with children.
Daniel Bekele, head of the commission, told Reuters on Tuesday that it was monitoring "the arrests of hundreds of Tigrayans in Addis Ababa".
Police have denied making ethnically motivated arrests, saying they are only targeting supporters of the rebellious Tigrayan forces fighting the central government.
Fasika Fanta, spokesperson for the Addis Ababa police, and government spokesman Legesse Tulu told Reuters they had no information on the arrests of U.N. staff.
"Those that have been detained are Ethiopians who violate the law," said Legesse.
The year-long conflict in northern Ethiopia between the government and Tigrayan forces loyal to the Tigray People's Liberation Front (TPLF) has intensified in recent weeks after he TPLF pushed south. Tigrayan forces and their allies have threatened to march on the capital.
Ethiopia declared a state of emergency on Nov 2. That permits the government to arbitrarily arrest, without a court order, anyone suspected of collaborating with a terrorist group. Parliament designated the TPLF as a terrorist group earlier this year.
Britain tightened its travel advice on Tuesday, advising citizens to leave Ethiopia while commercial flights are available, after the United States on Nov. 5 advised all citizens to leave Ethiopia as soon as possible.
Zambia evacuated non-essential staff from Ethiopia on Tuesday, its foreign ministry said.
