NAIROBI, Kenya (AP) — The sound of heavy weapons erupted across the Ethiopian border town, and immediately Filimon, a police officer, started to run.

Now, shaken and scared, he pauses when asked about his wife and two small children, ages 5 and 2. “I don’t know where my family is now,” he said, unsure if they were left behind in the fighting or are somewhere in the growing crowd of thousands of new refugees over the border in Sudan.

In an interview with The Associated Press by phone from Sudan on Thursday, the 30-year-old gave one of the first witness accounts from what experts warn is a brewing civil war with devastating humanitarian consequences. The conflict could draw in neighboring countries, too.

Filimon, who gave only his first name, said those attacking the Tigray regional town of Humera last week came from the direction of nearby Eritrea, though it was impossible to know whether the attackers were Eritrean forces.

Tigray regional leaders have accused Eritrea of joining the week-long conflict in the region at the request of Ethiopia’s federal government, which regards the Tigray government as illegal. Ethiopia has denied the involvement of Eritrean forces.

Filimon’s worries are far more immediate. After a day-long journey on foot with some 30 others fleeing, he has spent two days in Sudan, exposed to the sun and wind in a border town that is quickly becoming overwhelmed.

About 11,000 refugees have fled into Sudan, where authorities are preparing for up to 100,000, the United Nations refugee agency said Thursday.

Half of the refugees are children.

It was too early to collect statements from the refugees about the fighting, the agency said. Fleeing combatants were separated from civilians. Injured people — injured how, it was yet unclear - were being treated.

Tensions over the deadly conflict in Ethiopia are spreading well beyond its cut-off northern Tigray region, as the federal government said some 150 suspected “operatives” accused of seeking to “strike fear and terror” throughout the country had been detained. Hours later, police in Addis Ababa said they had arrested 242 people allegedly recruited “to cause terror in the capital.”

The government said the suspects “happen to be ethnically diverse,” but concerns remain high among ethnic Tigrayans amid reports of being singled out by authorities. “We don’t go to the office because they might also arrest us,” said one ethnic Tigrayan in the capital. “I'm in hiding, actually.”

Ethiopia’s parliament voted to remove immunity from prosecution for 39 top Tigray region officials, including its president, accusing them of revolting and “attacking the federal army.”

Ethiopia’s Nobel Peace Prize-winning Prime Minister Abiy Ahmed is rejecting international pleas for negotiation and de-escalation, saying that cannot occur until the ruling “clique” of the Tigray People’s Liberation Front is removed and arrested and its heavily stocked arsenal is destroyed.

In a bloody sign of how volatile Ethiopia’s tensions have become, Amnesty International said it had confirmed that scores of civilians were “hacked to death” in Mai-Kadra town in the Tigray region on Monday night. It cited photos and videos of bodies strewn in the streets and witnesses who saw them. Amnesty International said it has not been able to confirm who was responsible.

Abiy on Thursday asserted that the western part of the Tigray region had been liberated, and accused the TPLF rulers of seeking to “destroy Ethiopia.” He accused the TPLF forces of abuses. Defense Minister Kenea Yadeta said a transitional administration will be set up in “rescued” areas, the Ethiopian News Agency reported.

The Tigray regional president, Debretsion Gebremichael, called on the population to mobilize and defend themselves. Tigray TV, aligned with the TPLF, asserted that fighter jets had bombed the Tekeze hydroelectric dam.

What appeared to be a sudden slide toward civil war has been months in the making. Abiy after taking office in 2018 announced sweeping political reforms that won him the Nobel but marginalized the TPLF, which had dominated Ethiopia’s ruling coalition. The TPLF later left the coalition and in September held a local election in defiance of the federal government.

Each side now regards the other as illegal, and each blames the other for starting the fighting.

Rallies occurred in multiple cities in support of the federal government’s military offensive. At a blood drive in Addis Ababa, donor Admasu Alamerew said that “I also want to pass my message to those people who are causing conflict and urge them to fear God and make peace.”

Communications and transport links remain severed in the Tigray region, making it difficult to verify claims, while the U.N. and others warn of a looming humanitarian disaster as food and fuel run short for millions of people.

The conflict risks drawing in Ethiopia’s neighbors, notably Sudan as well as Eritrea, which is at bitter odds with the TPLF. Experts fear that the Horn of Africa, one of the world’s most strategic regions, could be destabilized despite Abiy’s past peacemaking efforts.

Meanwhile, more than 1,000 citizens of various countries are stuck in the Tigray region, the U.N. has said. Long lines have appeared outside bread shops, and supply-laden trucks are stranded at its borders. Fuel is already being rationed.

Over the border in Sudan, thousands of Ethiopian refugees waited, few possessions in hand, as authorities hurried to find a place to host them.

“It’s just countryside. There’s nothing there. Everything will have to be provided,” said Charles Franzen, disaster response director for the aid group World Relief, whose largest program is in Sudan. At first, he said, for people who were already in a fragile stage, there will be a “fair amount of human suffering.”