Armed groups join forces in Ethiopia in biggest threat yet to embattled Prime Minister Abiy Ahmed

Armed groups fighting Ethiopia's central government are swelling in numbers as they advance on the capital Addis Ababa, posing the biggest threat to embattled Prime Minister Abiy Ahmed's rule since a bloody year-long conflict began in the country's northern Tigray region a year ago.

Nine groups opposing the government -- a broad coalition of armed groups and political actors representing different regional and ethnic interests -- formed a new alliance on Friday "in response to the scores of crises facing the country" and to fight against the "genocidal regime of Ethiopia," according to a statement issued by organizers.

The new bloc, which calls itself the United Front of Ethiopian Federalist and Confederalist Forces, said in a signing event in Washington, DC, that it no longer recognized Abiy's government as legitimate and would seek to establish transitional arrangements, striving toward a democratic future.

The alliance includes fighters loyal to Tigray's former ruling party that once dominated the country, the Tigray People's Liberation Front (TPLF), known as the Tigray Defense Forces (TDF), who have been battling Ethiopia's military since Abiy ordered an offensive in the region last year.

Twelve months on, the fighting has left thousands dead, displaced more than 2 million people from their homes, fueled famine and given rise to a wave of atrocities. Now, with combined rebel forces edging closer to Addis Ababa and Ethiopian authorities announcing a nationwide state of emergency, fears are growing that the conflict could spiral into all-out war.

But top Ethiopian government officials have downplayed rebel advances, claiming they yield little popular support.

Ethiopia's attorney general Gedion Timothewos, who announced the state of emergency earlier in the week, said in a videoconference with reporters Friday that the members of the anti-government alliance, including the fighters loyal to the TPLF, are "deeply unpopular among the overwhelming majority of Ethiopians." He added the state of emergency was declared "out of an abundance of caution" based on intelligence that the TPLF might try to create havoc in the capital or in other cities.

Asked by CNN's David McKenzie about what conditions need to be met for the central government to engage with TPLF in any kind of talks, Timothewos said: "At the very least, the TPLF has to withdraw from Amhara and Afar regions where it's brutalizing innocent civilians."

In the same videoconference, Abiy's spokeswoman, Billene Seyoum, said, "the capital is moving about with a sense of normalcy" and accused international media outlets of misrepresenting the situation.

As the war and its impact on civilians deepens, the UN, United States, European Union, Ethiopia's southern neighbor Kenya, Canada and human rights groups have increased calls for an immediate and lasting ceasefire.

Ethiopia's government declared a unilateral ceasefire in June, when Tigrayan forces retook the regional capital Mekelle. But the TPLF categorically ruled out a truce, and the fighting has spread beyond Tigray's borders into the neighboring Amhara and Afar regions.

UN human rights chief Michelle Bachelet told CNN Wednesday she was "very concerned" about the recent escalation of violence in the multi-ethnic federation, "that could lead to a real civil war with a lot of bloodshed and with a lot more pain and suffering." It also risks fragmenting Ethiopia as a state, she said.

A joint investigation into the Tigray conflict by the UN Human Rights Office and Ethiopia's state-appointed human rights commission released Wednesday blamed all parties to the conflict for carrying out possible war crimes.

As Tigrayan fighters have pushed the front line further south, they have allied with the Oromo Liberation Army (OLA), a rebel group fighting for the rights of people from Oromia, Ethiopia's most populous region.

Last month, the Ethiopian military intensified airstrikes on Mekelle and other cities in Tigray. In recent days, Abiy has also pledged to bury his government's enemies "with our blood."

The rapid advance of the fighters, who said on Sunday they had seized Dessie and Kombolcha, two key towns on the road to Addis Ababa, has raised concerns among Ethiopia's leaders that the capital could fall.

It is unclear, though, whether the rebels have the firepower to take the city and there are conflicting reports as to how close they are to the capital.

An OLA spokesperson told CNN on Thursday that joint rebel fighters were still "weeks to months" away from taking the capital. They are about 160 kilometers (99 miles) from Addis Ababa, Odaa Tarbii said.

The question of entering the capital city is "purely based on what happens if it comes to negotiations," with the federal government, added Odaa, saying that the group hopes to avoid a direct military conflict in the densely populated city.

Abiy has urged citizens to take up arms and fight the Tigrayan forces. "Our people should march ... with any weapon and resources they have to defend, repulse and bury the terrorist TPLF," Abiy said in a Facebook post Sunday. The inflammatory post was later taken down by Facebook for inciting violence.

Addis Ababa's city administration was instructing residents to register their weapons and gather in local neighborhoods to "safeguard" their surroundings, Reuters reported.

Ethiopian state TV on Friday was broadcasting footage of crowds rallying in support of Abiy, waving Ethiopia's tricolor flag in the capital.