The UN High Commissioner for Human Rights, Michelle Bachelet, has urged the parties in the conflict in Ethiopia's northernmost Tigray regional state "to give clear and unambiguous orders" to their forces to take constant care to spare and protect the civilian population.

"The highly aggressive rhetoric on both sides regarding the fight for Mekelle (capital of Tigray regional state) is dangerously provocative and risks placing already vulnerable and frightened civilians in grave danger," the High Commissioner said in a statement.

"I fear such rhetoric will lead to further violations of international humanitarian law," she added, expressing alarm at reports of a heavy build-up of tanks and artillery around Mekelle, the capital city of Tigray province following the Government's issuance of a 72-hour ultimatum.

"Such rhetoric suggests possible breaches of the cardinal principles of distinction, proportionality and precaution in the conduct of hostilities that are designed to ensure the civilian population is protected."

Responding to allegations that the Tigray People's Liberation Front (TPLF), which ruled over the Tigray regional state, is stationing itself among civilians, Bachelet stated that under international law, parties to a conflict should take all possible measures to protect the civilian population under their control from the effects of attacks, namely by avoiding, to the extent feasible, locating military objectives in densely populated areas.

"I remind all parties to the conflict that the obligation to respect international law is not conditional on the other party's behaviour. All parties to the conflict are bound to respect international humanitarian law and human rights law as applicable. The protection of civilians is paramount," she stressed.

In particular, the High Commissioner recalled that it is prohibited to treat as a single military objective a number of distinct military objectives located in a densely populated area.

According to the statement, more than 40,000 people have fled from the Tigray region into neighbouring Sudan amid the ongoing fighting.

Since the early hours of Nov. 4, the Ethiopian government has been undertaking military operations against the TPLF, which rules over Ethiopia's northernmost Tigray regional state.

The federal government's operation followed the TPLF's attack on the Northern command base of the Ethiopian Defense Force, a division stationed in the region for over two decades and based in Mekelle city, capital of Tigray region.

Meanwhile, the Ethiopian government on Tuesday stressed that "large number" of Tigray Special Forces and the militia are surrendering as part of a 72-hour ultimatum which was given by the Ethiopian government for TPLF fighters to surrender peacefully to the Ethiopian National Defense Forces (ENDF).

"Using the government's 72-hour period, a large number of Tigray militia and special forces are surrendering. Many have surrendered through the Afar region, and the remaining forces are surrendering peacefully," the state of emergency task force, established by the federal government to watch over the ongoing military operations against the TPLF, said in a statement on Tuesday.

"The Ethiopian government would like to thank members of the Tigray Special Force and the militia who are responding to the call," the statement read.

"Those still under the control and captivity of the TPLF and are unable to surrender, are asked to disarm wherever they are and refrain from being exploited by the TPLF until the National Defense Forces rescue them," it added.

The Ethiopian government, which on late Sunday disclosed that its military operations in the northern Tigray regional state are now in its "final and crucial phase," as it announced a 72-hour ultimatum for the TPLF leaders to surrender to the Ethiopian defense force.