At least 16 UN workers have been "detained against their will" in war-torn Ethiopia, while British nationals have been told to leave the African nation immediately.
Since Ethiopia declared a state of emergency last week, the government has been able to arrest anyone suspected of being involved with a terrorist group without needing a court order.
The Tigray People's Liberation Front (TPLF) was called a terrorist group by the country's parliament earlier this year after fighting broke out in November 2020 when Prime Minister Abiy Ahmed announced a military offensive to overthrow the TPLF, who were Tigray state's regional ruling party.
The UN says its staff members detained in Addis Ababa are ethnic Tigrayan, amid reports the TPLF and its allies recently threatened to march on the capital.
It comes as the UK's Foreign Office (FCDO) urged British nationals to leave the country "while commercial routes are available" over fears the conflict could worsen further.
UN spokesman Stephane Dujarric said that in addition to the 16 staff members detained, another six were held and then released with no reason given as to why.
Deputy UN spokesman Farhan Haq added security colleagues have visited the workers who have been detained and that Ethiopia's foreign ministry has been asked for their immediate release.
Ethiopian government spokesman Legesse Tulu has not yet spoken about the detentions.
However, the government previously said it has been detaining people who are suspected of supporting the rival Tigray forces.
Thousands of people have been killed in over the last year in Ethiopia, with thousands also being detained and millions of people left displaced.
The FCDO has now issued the urgent warning for Britons while saying the conflict "has the potential to escalate and spread quickly and with little warning".
A statement on the department's website said: "The FCDO now advises against all travel to Ethiopia, except for Addis Ababa Bole International Airport (where advice remains against all but essential travel).
"The FCDO also advises you to leave Ethiopia while commercial routes are available."