Rebels from Ethiopia's war-hit Tigray said Monday the military had launched ground offensives "on all fronts" including in the northern region of Amhara.
Prime Minister Abiy Ahmed's office did not explicitly confirm the news, which follows widespread speculation that a major military push is imminent, but said the government had an obligation to protect citizens from the Tigray People's Liberation Front (TPLF).
"Abiy Ahmed's threatened offensive to reinvade Tigray has officially begun," said a statement issued by the TPLF, the region's former ruling party.
"On the morning of October 11, 2021, the Ethiopian military with the support of Amhara forces launched coordinated offensives on all fronts," the statement said.
"In addition to fielding hundreds of thousands of regular and irregular fighters, these genocidal forces are supported by heavy artilleries, tanks, rockets, drones and fighter jets, leaving no doubt about their annihilationist intent."
Abiy's government stresses that military operations in the north are targeting the TPLF, which it has officially designated a terrorist group, and not the population at large.
TPLF spokesman Getachew Reda said that despite the new offensive, army troops had yet to reach Tigray as of Monday morning.
He also said the TPLF was not aware of any involvement by Eritrean troops, which have previously backed up Ethiopia's military during the 11-month-old war.
The rebels' claims could not be independently verified, as many conflict-hit areas of Amhara are under a communications blackout.
"The Government of Ethiopia has a responsibility to protect its citizens in all parts of the country from any acts of terrorism," said Billene Seyoum, Abiy's spokeswoman.
"The government of Ethiopia will continue to counter the TPLF's destruction, violence and killings in the Amhara region and elsewhere."
Humanitarian and rebel sources told AFP over the weekend that Ethiopian troops had launched air and ground strikes as part of the first phase of an offensive that -- if confirmed -- would come just one week after Abiy was sworn in for a new five-year term.
The war erupted last November when Abiy -- winner of the 2019 Nobel Peace Prize -- sent troops into Tigray to topple the TPLF, who dominated national politics before he took power.
The move was in response to attacks on federal army camps by the TPLF, Abiy said, following months of tensions between the two sides.
Fighting has since spread to neighbouring Amhara and Afar and created what the UN calls an "immense humanitarian crisis" with hundreds of thousands of people driven into famine-like conditions.
The US has threatened sanctions against the warring parties if they fail to commit to a negotiated settlement.