NAIROBI, Kenya (AP) — Ethiopia’s prime minister on Friday defended military operations against the country’s well-armed Tigray region after accusing its government of a deadly attack on a military base this week, asserting that months of patiently trying to resolve differences have “failed” because of the leadership’s “criminal hubris and intransigence.”

Prime Minister Abiy Ahmed appeared to close the door on dialogue, which some experts and diplomats say is desperately needed. He asserted that the “large-scale law enforcement operation” has "clear, limited and achievable objectives: to restore the rule of law and the constitutional order.” He described the region's leadership as “fugitives from justice ... using the civilian population as human shields."

The northern Tigray region was increasingly cut off as Ethiopia's civil aviation authority said airports in the regional capital, Mekele, along with the regional cities of Shire, Axum and Humera were “closed for any services." And in Sudan, the acting governor of Kassla province said its border with northern Ethiopia has closed "until further notice” due to the tensions, the Sudan News Agency reported.

Alarm has grown as one of Africa's most powerful and populous countries nears civil war, which experts say would be catastrophic and destabilizing for the Horn of Africa. It was not clear who was taking the lead on any mediation; the African Union, based in Ethiopia, has not issued a statement.

Aid groups warned a humanitarian disaster is in the making if the fighting continues, with the COVID-19 pandemic just one of several crises.

Communications remained almost completely cut off in Tigray. They disappeared around the time that Abiy early Wednesday announced the military’s move in response to an alleged deadly attack by Tigray People's Liberation Front forces on a military base.

That attack was “the last straw,” Abiy said Friday.

The prime minister, who won the Nobel Peace Prize last year for his sweeping political reforms, now faces his greatest test as the TPLF, which dominated Ethiopia's government before he took office in 2018, has pushed back while feeling marginalized.

Both sides issued strong statements Thursday. Ethiopia’s army said it was deploying troops from around the country to Tigray, and the Tigray leader alleged that fighter jets had bombed parts of the regional capital. “We are ready to be martyrs,” he said. Casualties have been reported on both sides.

At least one fighter jet flew overhead but there was no confirmation it dropped bombs, a source in Ethiopia told The Associated Press, speaking on condition of anonymity because they were not authorized to speak to the media about the issue. Thursday saw heavy fighting and shelling, the source said, and roads to Tigray were closed.

A command post established by the federal government on Tigray said Friday that public meetings and moving in groups of more than four people were not allowed, and no one aside from law enforcement could bear arms.

The federal police asserted that its members guarding 22 locations throughout Tigray had came under attack from TPLF forces in recent days.

It remained challenging to verify either side’s version of events.

But some word began to emerge from the region. On Friday, the International Rescue Committee received its first message from colleagues in Tigray.

“There aren't active hostilities under way in the areas where we're working,” said George Readings, who leads the group's global crisis analysis. But “we know the situation is pretty tense."

Some 90,000 in Tigray receive International Rescue Committee services, and Readings worried about how conflict would affect “so many people already so vulnerable.”

Tigray receives refugees from neighboring Eritrea - Readings could not say whether that border was open - and the region has been hit hard this year by a locust outbreak.

“I should mention there has been flooding as well,” he said. “It's a really delicate situation.”

He said the IRC's Tigray operations confirmed having fuel available for the next month. “Then, there is a real question,” if travel remains restricted and fighting continues, Readings said.

It was not clear what, if any, powerful backers Tigray might have at the moment.

Tigray borders Eritrea, which fought a years-long border war with Ethiopia before the two countries made peace in 2018. The Tigray government and Eritrea don't get along, and the TPLF this week accused Eritrea of teaming up with Ethiopia's federal government to target it.

Eritrea remains one of the world's most closed-off nations, but its ambassador to Japan tweeted overnight that “TPLF’s push for militarization, proxy wars & reviving the rules of military engagement in the region must cease now.”

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Meseret reported from Addis Ababa, Ethiopia. Nona Elhennawy in Cairo contributed.