NEW YORK, Nov 9 (Reuters) - At least 16 United Nations staff and dependents have been detained in the Ethiopian capital Addis Ababa, a UN spokesperson said on Tuesday (Nov 9), amid reports of widespread arrests of ethnic Tigrayans.

"We are, of course, actively working with the government of Ethiopia to secure their immediate release," UN 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 UN staff.

"Those that have been detained are Ethiopians who violate the law," said Legesse.

The US State Department said Washington finds the reports of arrests of UN staff members "concerning", adding that harassment and detention on the basis of ethnicity is completely unacceptable.

"The reports do tend to suggest an arrest based on ethnicity and that is something that if confirmed, we would strongly condemn. So whatever we can do to secure the release of these individuals, we will be prepared to do," State Department spokesman Ned Price told reporters.

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 southward. 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.