ADDIS ABABA, Ethiopia — Renewed fighting in northern Ethiopia on Thursday effectively shattered a peace pact that ended a devastating two-year war in 2022, with rebel forces mobilizing for an armed struggle they hope will lead to the removal of the federal prime minister.

The main combatants are Ethiopian federal troops and fighters loyal to the Tigray People’s Liberation Front, or TPLF, an armed political group in Tigray, Ethiopia’s northernmost regional state.

The TPLF and Ethiopian federal troops waged war between November 2020 and November 2022, when a peace deal was signed in Pretoria, South Africa.

Eritrean troops fought alongside Ethiopian forces against the TPLF in that conflict. The civilian death toll was estimated by Ghent University researchers to be 500,000, including from violence, famine and the collapse of health services.

After both sides signed the Pretoria peace deal, a caretaker administration seen as loyal to Ethiopian Prime Minister Abiy Ahmed was installed in Mekelle, the Tigray capital. But tensions remained, with the TPLF maneuvering for political control in Mekelle.

This time, the TPLF appears to have mobilized widely, bringing together former foes in its stated goal of removing Abiy from power in Addis Ababa, the federal capital.

On Sunday, the TPLF and six other opposition groups announced that they had formed an alliance to overthrow Abiy’s governing Prosperity Party, which was reelected in June polls that were boycotted by major opposition groups.

Both sides had been accusing each other of bad faith, and for months some civilians in Tigray expected a return to armed hostilities. In May, the TPLF forced out regional leader Tadesse Werede, who reported to Abiy, and replaced him with a new council led by TPLF leader Debretsion Gebremichael, who led the Tigrayans in the previous conflict.

Ethiopian federal authorities accused the TPLF of seeking to build an alliance with neighboring Eritrea to destabilize Ethiopia. The TPLF accused Ethiopian authorities of conducting drone attacks in Tigray. Eritrea said that it was alarmed by Abiy’s repeated assertions of his wish for sovereign access to the Red Sea via Eritrea.

Both sides deny responsibility for launching this round of hostilities, and most of the fighting is believed to be in remote areas of often ragged, mountainous territory. On Wednesday, TPLF fighters seized the airport in Mekelle from federal police, and national carrier Ethiopian Airlines canceled flights there and elsewhere in the region.

The Ethiopian News Agency, the official news organization of the Ethiopian government, described the TPLF as a “Trojan horse,” saying that the group’s “repeated attempts to incite conflict” defy the government’s “patience, concessions and magnanimity.”

The coalition formed by the TPLF and six other opposition groups said that it would be known as the Ethiopian Peoples’ Forces Alliance for Survival. In addition to the TPLF, the others include the Amhara Fano National Movement, the Oromo Liberation Army, the Ogaden National Liberation Front, the Afar Revolutionary Democratic Unity Front, the Benishangul Peoples’ Liberation Movement and the Gumuz Peoples’ Democratic Movement.

That alliance, which unites some groups previously opposed to each other, may put pressure on Abiy, according to Kjetil Tronvoll, an academic analyst of Ethiopia at Oslo New University College.

“The situation now differs substantially from the 2020-2022 war on Tigray,” he said in an analysis posted on X. “This time around Fano is an ally and Eritrea a backer. Supply lines are also secured through Eritrea.”

The African Union and a key regional bloc known as IGAD called for de-escalation of hostilities. U.S. Ambassador Ervin J. Massinga said in a statement that he felt disappointed by the TPLF’s “poor decision to launch a large-scale offensive.”

His statement said that the TPLF’s “unwinnable fight does nothing for the people. Other armed groups would be wise to avoid this.” A TPLF official, Amanuel Assefa, said the statement was unfair.

Abiy has been praised by many for his ambitious infrastructure projects that seek to turn Addis Ababa into a world-class city. To his supporters, the prime minister is a renaissance man trying to reimagine the old greatness of Ethiopia.

Abiy rose from relative obscurity to power in 2018 as a reform-minded pragmatist. Ties with Eritrea, which broke away from Ethiopia in 1993 after decades of brutal guerrilla warfare, had been cold since the 1990s, and Abiy’s efforts to repair relations with Eritrean President Isaias Afwerki helped him win the 2019 Nobel Peace Prize.

A year later, Abiy confounded expectations by launching a military operation against the TPLF.

Some of Abiy’s critics now see him as a provocateur whose actions could lead to hostilities in the Horn of Africa. His push for sovereign access to the Eritrean seaport of Assab has reignited tensions with Eritrea, which shares a border with Tigray. Abiy also angered Somalia by trying to negotiate access to the sea via the territory of Somaliland.

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Rodney Muhumuza reported from Kampala, Uganda.