NAIROBI, Kenya (AP) — At least 30 armed Ethiopian troops and “large numbers” of refugees fleeing the fighting in Ethiopia’s northern Tigray region have crossed the border into Sudan, the state-run SUNA news agency reported, while one diplomat on Tuesday said hundreds of people have been reported killed on both sides of Ethiopia's week-long conflict.

As the African Union urged an immediate cease-fire, Nobel Peace Prize-winning Prime Minister Abiy Ahmed again vowed that his military will bring a speedy end to the fighting in the heavily armed Tigray region and the removal of its leadership, which his government regards as illegal. With the region almost completely cut off, it remained difficult to confirm either side's claims. Each blames the other for sparking the conflict.

Sudan, which has sent more than 6,000 troops to the border, has been under pressure from the international community to help make peace and from the Ethiopian government, which seeks to cut Tigray off from the outside world.

The troops from Ethiopia's Amhara region neighboring Tigray fled into Sudan’s Qadarif province Monday evening, the SUNA report said, citing witnesses. Local authorities have started to prepare a refugee camp for the fleeing Ethiopians, it said, while aid groups warn of a brewing humanitarian crisis affecting millions of people at the heart of the Horn of Africa region.

The Ethiopian troops turned themselves and their weapons in, and appealed for protection as fighting raged over the border, said a Sudanese military official on condition of anonymity because he was not authorized to brief reporters.

Abiy described his government's military campaign in the Tigray region as “law enforcement operations” that he said will end as soon “as the criminal junta is disarmed, legitimate administration in the region restored, and fugitives apprehended and brought to justice — all of them rapidly coming within reach." On Monday a military official said the air force was “pounding targets with precision."

The African Union Commission chairman, Moussa Faki Mahamat, has called for the “immediate cessation of hostilities.” In a statement Monday, he said the AU, based in Ethiopia, is ready to support an “inter-Ethiopian effort in the pursuit of peace and stability.”

Abiy has shown no sign of opening talks with the Tigray People's Liberation Front, which once dominated Ethiopia’s ruling coalition. Feeling marginalized by Abiy’s political reforms after he took office in 2018, it broke away last year as the prime minister sought to transform the coalition into a single Prosperity Party. The TPLF defied the federal government by holding a local election in September.

Diplomats and others assert that the conflict in Tigray could destabilize the region and other parts of Ethiopia, Africa’s second-most populous country with 110 million people. Ethiopia has scores of ethnic groups and other regions that have sought more autonomy even as Abiy, who won the Nobel just last year, tries to hold the country together with exhortations of national unity.

Several hundred people reportedly have been killed on both the Ethiopian government side and the Tigray regional government side, a diplomat in the capital, Addis Ababa, told The Associated Press.

More than 150 citizens of European Union countries alone are thought to be in the Tigray region, which is increasingly cut off with airports and roads closed and communications largely severed, and governments are trying to ensure their consular protection, the diplomat added, speaking on condition of anonymity.

“There are so many uncertainties,” the diplomat said. “How far can Abiy go with this operation while keeping the possibility of, in the end, having a more or less peaceful solution? You need the support of the people.”

Experts worry that the longer the conflict lasts, the more difficult it will be for the federal government to bring the Tigray region back to Ethiopia's federation of regional states.

Aid groups warn the humanitarian needs will grow.

“They need to prioritize de-escalation and allow humanitarian work to happen,” George Readings, who leads global crisis analysis for the International Rescue Committee, told the AP, adding that new populations will be made vulnerable.

The group has one month left of fuel to run water pumps for 90,000 refugees, he said. Without it, “then there just won’t be clean water to drink, wash hands, deal with COVID,” he said. The group also feeds undernourished children, and “we don’t know if, or when, or how we'll be able to resupply.”

Ethiopia's federal government continued to assert military gains Tuesday, with the defense forces saying they had seized the Humera airport in Tigray, near the border with Sudan and Eritrea, the state-affiliated Fana Broadcasting Corporate reported.

Eritrea has said little publicly on the fighting but has blamed the TPLF, a longtime rival, for starting it. Eritrea's ambassador to Kenya and Tanzania, Beyene Russom, scoffed in a tweet at the idea the TPLF, with “a huge arsenal of a quantity & quality bigger than most of African countries,” would negotiate with Ethiopia's federal government. “Then what? Allow it to secede? Rule Ethiopia again?” he asked.

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Magdy reported from Cairo.