African peace envoys were due to meet Ethiopian Prime Minister Abiy Ahmed on Friday, a day after he said the military was beginning the "final phase" of an offensive in the northern Tigray region that rights groups fear could bring huge civilian casualties.
The government had given the Tigray People's Liberation Front (TPLF) until Wednesday to lay down their arms or face an assault on Mekelle, the regional capital of 500,000 people. The United Nations says 200 aid workers are also in the city.
The envoys were due to meet Abiy at 11 a.m. (0800 GMT), Redwan Hussein, spokesman of the government's State of Emergency Task Force for the Tigray conflict, said.
The envoys were in Addis Ababa "with a view to helping to mediate between the parties to conflict" in Ethiopia, South African President Cyril Ramaphosa, who is also the AU chair, said earlier this week.
Abiy, who won last year's Nobel Peace Prize for ending a two-decade standoff with Eritrea, has said he will not talk with TPLF leaders until they are defeated or give up.
Thousands of people are already believed to have died amid air strikes and ground fighting since the war began on Nov. 4. The U.N. estimates 1.1 million Ethiopians will need aid as a result of the conflict.
The conflict has sent shockwaves through the Horn of Africa. More than 43,000 refugees have fled to Sudan. TPLF rockets have hit the capital of neighbouring Eritrea.
Reuters was unable to reach the TPLF for comment on Friday morning, but two diplomats said fighting raged in several areas outside Mekelle.
With phone and internet connections shut off to the region and access to the area tightly controlled, verifying claims by all sides has been impossible.
There was no indication that the Ethiopian military had entered the city of Mekelle. The TPLF has previously said it was digging trenches around the city. Reuters was unable to verify those claims.
Finance Minister Ahmed Shide said on Thursday that the government was trying to make people in the city aware of the military operation.
"We have made the people of Mekelle to be aware of the operation by deploying military helicopters and dropping pamphlets in Tigrinya and also in Amharic so that they protect themselves against this," he told France24.
Kenneth Roth, executive director of Human Rights Watch, said such efforts were not akin to protecting civilians from harm.
"Warnings don't absolve the Ethiopian military of the duty to protect civilians during military operations in urban areas," Roth tweeted on Thursday. Urging the TPLF not to deploy its forces among civilian populations in the city of Mekelle, he added: "Violations by one side don't justify violations by the other."
Abiy's office said on Thursday that authorities were opening a humanitarian access route, but the U.N. said it had no information on the route and the region was blocked to aid groups.
Tigrayans, who make up about 6% of Ethiopia's 115 million-strong population, dominated the government until Abiy took power two years ago.
Pledging to unite Ethiopians and introduce freedoms after years of state repression, Abiy jailed senior Tigrayan officials. The region saw that as discrimination.
Abiy accuses Tigrayan leaders of starting the war by attacking federal troops at a base in Tigray three weeks ago. The TPLF have described the attack as a pre-emptive strike.
Tigrayan forces have large stocks of military hardware and number up to 250,000 men, experts say, while the region has a history of guerrilla resistance.
Even before war broke out, as resentment in Tigray against the federal government grew, Tigrayans adopted a slogan from the TPLF: "nobody will kneel down".