Clashes erupted in early July prompting the authorities in Addis Ababa on August 4 to declare a six-month state of emergency. AFP
"We are very concerned by the deteriorating human rights situation in some regions of Ethiopia," UN Human Rights Office spokeswoman Marta Hurtado told reporters in Geneva.
In Amhara region, following a flare-up in clashes between the Ethiopian military and the regional Fano militia, and the declaration of a state of emergency on August 4, the situation worsened considerably.
At least 183 people have been killed in clashes since July, according to information gathered by the UN Human Rights Office.
Tension in the northern region ratcheted up this year after the end of a devastating war in neighbouring Tigray that also drew in fighters from Amhara.
In April the federal government announced it was dismantling regional forces across the country.
The move triggered protests by Amhara nationalists who said it would weaken their region.
Clashes erupted in early July between the national army and local fighters known as Fano, prompting the authorities in Addis Ababa on August 4 to declare a six-month state of emergency.
The status gives the authorities broad powers to arrest suspects without a court order, impose curfews and ban public gatherings, Hurtado said.
"We have received reports that more than 1,000 people have been arrested across Ethiopia under this law. Many of those detained were reported to be young people of Amhara ethnic origin suspected of being Fano supporters," she said.
"Since early August, mass house-to-house searches have reportedly been taking place.
"We call on the authorities to stop mass arrests, ensure that any deprivation of liberty is judicially reviewed, and release those arbitrarily detained."
She added: "We call on all actors to stop killings, other violations and abuses."