NAIROBI, Kenya (AP) — Ethiopia's prime minister said Thursday the army has been ordered to move on the embattled Tigray regional capital after his 72-hour ultimatum for Tigray leaders to surrender ended, and he warned residents to stay indoors and disarm.

The statement by Prime Minister Abiy Ahmed's office means tanks and other weaponry can now close in on Mekele, a city of some half-million people. His government has warned of “no mercy” if residents don't move away from the Tigray leaders in time.

The military offensive “has reached its final stage" after three weeks of fighting, the new statement said.

It asserts that thousands of Tigray militia and special forces surrendered during the 72-hour period. “We will take utmost care to protect civilians,” it says.

The United Nations has reported people fleeing the city, but communications and transport links remain severed to Tigray, and it’s not clear how many people in Mekele received the warnings.

The alarmed international community is calling for immediate de-escalation, dialogue and humanitarian access. Abiy on Wednesday, however, rejected international “interference.”

It remains difficult to verify claims in the fighting that erupted Nov. 4 between Ethiopian forces and the heavily armed forces of the Tigray People's Liberation Front, which once dominated Ethiopia's government but has been sidelined under Abiy's rule. The two governments now regard each other as illegal.

The U.N. says shortages have become “very critical” in the Tigray region as its population of 6 million remains sealed off.

Fuel and cash are running out, more than 1 million people are now estimated to be displaced and food for nearly 100,000 refugees from Eritrea will be gone in a week, according to a new report released overnight. And more than 600,000 people who rely on monthly food rations haven’t received them this month.

Travel blockages are so dire that even within Mekele the U.N. World Food Program cannot obtain access to transport food from its warehouses there.

Human Rights Watch is warning that “actions that deliberately impede relief supplies” violate international humanitarian law.