Ethiopian Prime Minister Abiy Ahmed announced Thursday that the final operation to take the capital of the rebellious Tigray province could begin after a 72-hour ultimatum to surrender had expired.

Ethiopia’s military intervened in the rugged northern province after local forces there attacked an army base and made off with military equipment Nov. 3, sparking three weeks of unrest in which federal forces have taken over much of Tigray.

With communications to the province cut, it was impossible to verify whether the military operation against the regional capital of Mekele had begun. Government forces said they had surrounded the city of 500,000 with tanks from 30 miles away.

“The Ethiopian National Defense forces have now been directed to conclude the third and final phase of our rule of law operation,” said the statement from the prime minister’s office. “We call on the people of Mekele and its environs to disarm, stay at home and stay away from military targets, and take all necessary precautions.”

The government campaign is against the political party controlling the province, the Tigrayan People’s Liberation Front, which once dominated the coalition that ruled the country for nearly 30 years. With the rise of Abiy, they retreated to their power base in Tigray, and in recent months relations with the central government have soured dramatically.

At least 40,000 refugees have fled the fighting into neighboring Sudan, and there have been reports of hundreds of civilians massacred. Photos blazed across social media of people with bullet and machete wounds.

“It is vital that humanitarian services, as well as basic services, are provided,” said Aaron Maasho, senior adviser and spokesman for the Ethiopian Human Rights Commission in the capital, Addis Ababa.

Some advocates in the city worried soldiers advancing on Mekele would trigger indiscriminate violence.

“A bloodbath,” said one, who spoke on the condition of anonymity, fearing for their safety. Without Internet access, it was unclear how many residents heard the prime minister’s warning to stay home.

The Ethiopian government has insisted its quarrel is only with the TPLF and not against the Tigrayan people and said the grace period was for the local forces to surrender.

“The last peaceful gate which had remained open for the TPLF clique to walk through has now been firmly closed as a result of TPLF’s contempt for the people of Ethiopia,” the statement added.

In messages to media outlets, the TPLF leadership has insisted that government forces have suffered several defeats. The Ethiopian government has countered by reporting surrenders among TPLF forces.

There has been widespread international concern about the campaign and calls for mediation that have been rejected by Abiy, last year’s Nobel Peace Prize winner, who has said the operation is an internal matter.

President-elect Joe Biden’s national security adviser nominee, Jake Sullivan, urged dialogue this week facilitated by the African Union.

“I’m deeply concerned about the risk of violence against civilians, including potential war crimes, in the fighting around Mekelle in Ethiopia,” he said on Twitter.

The U.N. refugee agency has warned that a “full-scale humanitarian crisis” is unfolding in Tigray, and there are fears that food and water may be running out in this province of 6 million.

As supplies precariously dwindled, aid workers said they had no way to reach people who had been forced from their homes for weeks.

Thousands — including pregnant women and those battling illness — were crossing the Sudanese border each day in search of safety, they said. Spouses have been separated. Children have lost touch with their parents.

The prime minister’s office said in a Thursday statement that it would provide essentials to the rush of displaced citizens and clear the way for humanitarian groups, adding that the government “stands to support all Ethiopians that have fled to return to their communities.”

The pledge appeared to open a new path for desperately needed assistance, said Nigel Tricks, regional director of the Norwegian Refugee Council in Nairobi.

“People have gone from having a roof over their head,” he said, “to absolutely nothing.”

Lesley Wroughton contributed to this report.