NAIROBI, Kenya (AP) — A university official says the latest airstrike by Ethiopia’s military has struck the school in the capital of the defiant Tigray region and caused major damage, while the United States says neither side in the conflict is heeding calls for de-escalation.

The senior official described Thursday’s airstrike in an email shared with The Associated Press. It was not immediately clear if anyone was killed or wounded in the airstrike in Mekele.

“How on earth” can a government bombard its own people, the senior official asked. The AP is not naming the official because they could not be reached directly.

There was no immediate comment from Ethiopia’s government, which has been fighting the Tigray regional forces since a Nov. 4 attack on a military base there. Ethiopia’s government has acknowledged carrying out airstrikes. The Tigray regional government has acknowledged firing missiles.

Each side regards the other as illegal regards the other as illegal, the result of a falling-out between Nobel Peace Prize-winning Prime Minister Abiy Ahmed and the Tigray leaders who once dominated the country's ruling coalition.

With communications to the region severed, no one knows how many people have been killed, and verifying either side’s claims is challenging.

“At this point, neither party, from what we hear, is interested in mediation,” the top U.S. diplomat to Africa, U.S. Assistant Secretary of State Tibor Nagy, told reporters Thursday evening.

Nagy said of the airstrike: “From what you say, I certainly hope it’s not true.”

Alarmed by the potential for disaster in Ethiopia and beyond, 17 U.S. senators urged Secretary of State Mike Pompeo in a letter Thursday to engage Abiy directly to push for an immediate cease-fire.

Ethiopia's government has said it is marching in a final push to Mekele, the Tigray capital, with the goal to arrest the ruling “clique” from the region's Tigray People's Liberation Front. The TPLF infuriated Abiy's government when it objected to the pandemic-related postponement of national elections until next year and held its own election in September.

Now, deadly fighting continues in a heavily armed region of some 6 million people, a clash some observers have compared to an inter-state war at the heart of the strategic Horn of Africa.

While Abiy's government rejects urgent international calls for dialogue, a humanitarian disaster is unfolding as food, fuel and medical supplies run desperately short in the Tigray region. Roads are blocked and airports closed.

More than 30,000 refugees have fled to Sudan, and the fighting has moved close to nearly 100,000 refugees from Eritrea at camps in northern Tigray.

“Electricity continues to be cut off. Fuel for generators has run out. That leaves 96,000 Eritrean refugees in Ethiopia without clean water,” United Nations spokesman Stephane Dujarric told reporters.

"A staggering number of people are crossing from Ethiopia into Sudan. Every. Single. Day," the U.N. refugee agency tweeted.

Refugees in Sudan said the fighting erupted so quickly they barely knew what they were fleeing.

“We didn’t know about war or when did it start,” said one, who gave her name as Terhas. She said that on the way to Sudan with her children, “we saw a lot of dead bodies,” while upon their weary arrival, “we didn't find food.”

Nearly half of the refugees are children, and the United Nations called the conditions they are facing “extremely harsh."

Asked about efforts to open humanitarian corridors, the U.S. ambassador to Ethiopia, Michael Raynor, told reporters that the TPLF “did not really engage on that possibility.” Meanwhile, a senior Ethiopian official, Redwan Hussein, said the government plans a fact-finding mission into the humanitarian situation that “will not take more than a week.”

The fighting also threatens to suck in or destabilize Ethiopia's neighbors, which include Sudan, Somalia and Eritrea, whose capital came under rocket attack from the TPLF over the weekend. Eritrea has remained largely silent while the TPLF accuses it of entering the conflict at Ethiopia's request.

Nagy, the assistant secretary of state for African affairs, told reporters that the U.S. has been in contact with Eritrean officials to urge their “continued restraint.”

“Internationalizing the conflict, that is one absolute danger that we are doing our best, the entire region is doing its best, to avoid,” he said.