NAIROBI, KENYA -- Ethiopia's situation is "spiraling out of control with appalling impact on civilians" and urgently needs outside monitoring, the United Nations human rights chief warned Wednesday, but Ethiopia rejects calls for independent investigations into the deadly fighting in its Tigray region, saying it "doesn't need a babysitter."

The government's declaration came amid international calls for more transparency into the month-long fighting between Ethiopian forces and those of the fugitive Tigray regional government that is thought to have killed thousands, including civilians. At least one large-scale massacre has been documented by human rights groups, and others are feared.

Senior government official Redwan Hussein told reporters on Tuesday evening that Ethiopia will invite assistance only if it feels that "it failed to investigate." To assume it can't carry out such probes "is belittling the government," he said.

Frustration is growing as the northern Tigray region remains largely cut off from the world, with food and medicines desperately needed by the population of 6 million -- some 1 million now thought to be displaced.

The lack of transparency, with most communications and transport links severed, complicates efforts to verify the warring side's claims.

It also hides the extent of atrocities feared to have been committed since Prime Minister Abiy Ahmed on Nov. 4 announced that fighting had begun with the Tigray People's Liberation Front, which dominated Ethiopia's government for nearly three decades before he came to power and sidelined it.

Each government now regards the other as illegal, as the TPLF objects to the postponement of national elections until next year because of the COVID-19 pandemic and sees Abiy's mandate as expired.

UN human rights chief Michelle Bachelet called the situation "exceedingly worrying and volatile" with fighting reported to continue in areas surrounding the Tigray capital, Mekele, and the towns of Sheraro and Axum, "in spite of government claims to the contrary."

"We have corroborated information of gross human rights violations and abuses including indiscriminate attacks against civilians and civilian objects, looting, abductions and sexual violence against women and girls," Bachelet told reporters. "There are reports of forced recruitment of Tigrayan youth to fight against their own communities."

However, she said, "we have been unable to access the worst affected areas."

Ethiopia's government objects to what it calls "interference," from efforts at dialogue to delivering aid, drawing on its history as the rare African country never colonized, a source of deep national pride.

The government on Tuesday said its forces had shot at and detained UN staffers who allegedly broke through checkpoints while trying to reach areas where "they were not supposed to go."

The incident "is really costly" because it further delays humanitarian operations for people in Tigray who have been waiting five weeks for aid, UN humanitarian spokesman Saviano Abreu told The Associated Press.

He said the six-member UN team, which was detained in Humera and released two days later, was the first sent into Tigray and was carrying out security assessments along roads that had been previously agreed upon with Ethiopia's government. Such assessments are crucial before aid can be moved in.

"Now we have to work out additional operational details with the government," especially on security, Abreu said, repeating the UN's call for unfettered, unconditional access.

The top U.S. diplomat for Africa, Tibor Nagy, tweeted that "we strongly urge all parties to safeguard humanitarian workers in and around Ethiopia's Tigray region. We continue to urge immediate and unhindered humanitarian access throughout Tigray."

The shooting occurred a week after the UN and the government signed a deal to allow humanitarian access. The deal, crucially, allows aid only in areas under federal government control.

Needs are critical. Mekele, a city of a half-million people, is "basically today without medical care," the director-general of the International Committee for the Red Cross, Robert Mardini, told reporters on Tuesday. The Ayder Referral Hospital has run out of supplies, including fuel for generators.

"Doctors and nurses have been forced to make horrible life and death decisions," Mardini said. "They suspended intensive care services and are really struggling to take care like delivering babies or providing dialysis treatment."

A joint ICRC-Ethiopian Red Cross convoy with supplies for hundreds of wounded people is ready to go to Mekele, pending approval, he said. It would be the first international convoy to reach the city.

While the risk of insecurity remains in the Tigray capital, there is no active fighting, Mardini said.

Overall, he said, "people in Tigray have been cut off from services for nearly a month. They have had no phone, no internet, no electricity and no fuel. Cash is running out. This of course adds to the tension."

In neighbouring Sudan, nearly 50,000 Ethiopian refugees now take shelter. Some resist being moved to a camp away from the border, in the hope that missing family members, separated by the fighting, can be found.

"How can we go?" asked one refugee, Haile Gebremikeal. "If we can stay here for one or two months, if they give us a chance, we can look for our family or our family can look for us. There are no telephones, no internet. We don't have anything."

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AP journalists Edith M. Lederer at the United Nations, Fay Abuelgasim in Village 8, Sudan, and Nadine Achoui-Lesage in Geneva contributed.