The Ethiopian military will begin the “final phase” of an offensive in the northern Tigray region, Prime Minister Abiy Ahmed has said in a statement, hours after an ultimatum for the Tigrayan forces to surrender expired.

“The 72-hour period granted to the criminal TPLF clique to surrender peacefully is now over and our law enforcement campaign has reached its final stage,” he tweeted on Thursday, referring to the Tigrayan People’s Liberation Front (TPLF).

Abiy said the army has been ordered to move on the embattled Tigray capital, Makelle and warned its residents to “stay indoors”.

The statement by the prime minister’s office means tanks and other weaponry can now close in on the city of some half a million people.

His government has warned of “no mercy” if residents do not move away from the Tigray leaders in time. “We will take utmost care to protect civilians,” it says.

The new statement asserts that thousands of Tigray militia and special forces surrendered during the 72-hour period.

The Reuters news agency said it was not immediately able to reach the Tigrayan forces for comment.

Claims by all sides have been impossible to verify because phone and internet connections to the region are down and access to the area is tightly controlled.