Ethiopia's capital Addis Ababa could fall within "months if not weeks", a military group allied with Tigrayan rebels told AFP on Wednesday.
The Tigray People's Liberation Front (TPLF), which has been fighting Prime Minister Abiy Ahmed's government for a year, has claimed significant territorial gains in recent days, along with its ally the Oromo Liberation Army (OLA).
In Washington, the US State Department said it was sending Jeffrey Feltman, special envoy for the Horn of Africa, to the country this week.
Earlier on Wednesday, OLA spokesman Odaa Tarbii said his group intended to topple Abiy's government, calling his removal "a foregone conclusion."
Ethiopia declared a nationwide state of emergency on Tuesday and ordered residents of the Addis Ababa to prepare to defend their neighbourhoods.
"They are enemies of Ethiopia and they need to (be) dismissed, and to do that all of us need to cooperate with the state of emergency," said Azmeraw Berhan, a self-employed man.
TPLF spokesman Getachew Reda said the measures amounted to a "carte blanche to jail or kill Tigrayans at will".
'Crimes against humanity'
A joint investigation by the office of UN rights chief Michelle Bachelet and the Ethiopian Human Rights Commission (EHRC), published on Wednesday, found evidence of "serious abuses and violations" by all sides in the conflict.
"The gravity and seriousness of the violations and abuses we have documented underscore the need to hold perpetrators accountable on all sides," Bachelet said.
The report, which covers the period from November 3, 2020, through to June, pointed to extra-judicial executions, endemic torture and sexual violence among other abuses, and said that "a number of these violations may amount to crimes against humanity and war crimes".
It detailed reports of gang rapes against women and girls, as well as men and boys.
It recorded the deaths of at least 29 civilians in shelling by Ethiopian forces targeting Tigray's capital Mekele on November 28, as well as revenge killings in Mai-Kadra following the town's capture by federal and Amhara forces after a massacre of ethnic Amhara residents last year.
Bachelet's office said it had also tracked abuses committed after the period covered in the report, including the deaths of 47 civilians at the hands of TPLF fighters in the village of Chenna in Amhara in September.
Abiy said the report presented no evidence of genocide but Bachelet said the findings were not so clear-cut and called for further investigation.
International alarm
The 2019 Nobel Peace laureate promised a swift victory, but by late June the rebels had retaken most of Tigray and expanded into the neighbouring regions of Afar and Amhara.
In recent days the TPLF has claimed control of two key cities in Amhara, about 400 km north of Addis Ababa.
The government has denied claims of TPLF territorial gains which, if confirmed, would represent a major strategic advance.
Much of northern Ethiopia is under a communications blackout and access for journalists is restricted, making battlefield claims difficult to verify independently.
The escalating conflict has sparked alarm among the international community, with thousands killed and hundreds of thousands forced into famine-like conditions, according to the UN.
