Ethiopian military forces are set to enter the "final phase" of an operation to take down the leadership of the Tigray People's Liberation Front.

Ground forces have been given the order to march into the Tigray capital of Mekelle.

Prime Minister Abiy Ahmed said the military would be closing down the "last peaceful gate" that has remained open for any front member that wished to surrender. Abiy - a Nobel Peace Prize awardee - claimed thousands of front members had already surrendered but many continued to threaten to destabilize the government.

None of Abiy's claims and those made by the front have been confirmed because the region remains in a communications blackout. Mobile phones, the internet and landlines are down.

Abiy issued an ultimatum earlier this week for the regional group to surrender to federal forces within 72 hours.

Ethiopia military officials expect to capture the regional capital by Saturday and surround it with tanks. Remaining civilians in the area have been warned of artillery fire as the military prepares a "no mercy" assault.

"Great care will be given to protect innocent civilians from harm. We call on the people of Mekelle and its environs to disarm, stay at home and stay away from military targets and take all necessary precautions," Abiy said in a statement.

Humanitarian workers in the region said most of the city was calm and quiet but people were "on edge." The Ethiopia government said some front forces may be using schools and churches as shelters.

The conflict escalated in early November. Federal forces launched attacks to disarm the group after it allegedly destroyed several government camps.

More than 42,000 refugees have fled - with most crossing into neighboring Sudan. The United Nations said the conflict had caused a "full-scale humanitarian crisis."

World leaders called on Abiy to find a peaceful approach. Human rights groups have called on the government to allow nonprofit organizations to enter the region to help civilians caught in the crossfire.