At least two rockets were fired from Ethiopia into neighboring Eritrea overnight Saturday as the conflict between regional rulers in Ethiopia’s northern Tigray state and the federal government of Prime Minister Abiy Ahmed spilled across the border, further raising fears that more countries in the Horn of Africa could be drawn into the conflict.

In a major escalation of a two-week-old conflict, Tigray’s president, Debretsion Gebremichael, said his forces had fired missiles at Eritrea’s capital, Asmara, because it had sided with Ahmed’s government in Addis Ababa.

“As long as troops are here fighting, we will take any legitimate military target and we will fire,” he told the Associated Press. He accused Eritrea of sending troops into the Tigray region as Ethiopian troops were deployed.

“We will fight them on all fronts with whatever means we have,” he said. On Friday, rockets were also fired by Tigray at two airports in the neighboring state of Amhara.

The U.S. Embassy in Asmara reported a series of loud noises were heard in the Eritrean capital but said there was no indication that the main international airport was struck.

“Unconfirmed reports indicate they may have been explosive devices believed to be in the vicinity of Asmara international airport,” the embassy said in a security alert to U.S. citizens.

There were no reports of casualties or damage.

The conflict erupted on Nov. 4 when Abiy accused the Tigray People’s Liberation Front, the powerful faction that governs the northern state, of crossing a “red line” by attacking federal military bases and ordered troops into the area.

Abiy has ignored international calls for an immediate de-escalation and pushed back at efforts by the African Union to moderate.

Tibor Nagy, the U.S. assistant secretary of state for African affairs, condemned “the TPLF’s unjustifiable attacks” against Eritrea and “its efforts to internationalize the conflict in Tigray.”

Abiy, in an apparent rebuttal to the Tigrayan claim that Eritrea is involved, tweeted that “Ethiopia is more than capable of attaining the objectives of the operation by itself.” He did not refer directly to the rocket attacks on Eritrea.

Abiy won the Nobel Peace Prize last year for restoring ties with Eritrea, ending a nearly 20-year military stalemate after the 1998-2000 border war. But despite peace between the two governments, animosity between Eritrea and the TPLF remains. The TPLF dominated the coalition ruling Ethiopia for decades until Abiy’s rise to power.

The U.N. refugee agency has warned of a humanitarian disaster in Ethiopia. The agency said Sunday that more than 20,000 refugees had crossed into Sudan. The agency has shown video of hundreds of refugees streaming through the Hamdayet border crossing in eastern Sudan, most of them children.

Communications and transport links with Tigray have been cut. The United Nations has warned that millions are at risk as food and fuel supplies run low.

Fears are growing of ethnic-based targeting. The TPLF has denied allegations that scores of civilians were hacked to death by its irregular militia last week in the town of Mai-Kadra in southwestern Tigray. In a report last week, rights group Amnesty International said it had confirmed the massacre of “a very large number” of civilians, many of them from the neighboring state of Amhara.

The conflict has killed hundreds of people on both sides. The TPLF’s military force and local militia are well equipped from the two-year war with Eritrea and the guerrilla war to topple Marxist dictator Mengistu Haile Mariam in 1991.

Amid the fighting in the north, analysts have warned of a security vacuum elsewhere in the country where ethnic violence has escalated since Abiy took over in 2018. Abiy introduced political reforms that also lifted the lid on long-repressed tensions among the many ethnic groups in the country.

Separately, gunmen in western Ethiopia killed at least 34 people in an attack on a bus on Saturday, the Ethiopian Human Rights Commission said in a statement. The “gruesome” attack took place in the Benishangul-Gumuz region, the commission said.

“The attack is a grim addition to the human cost which we bear collectively,” commission head Daniel Bekele said in a statement.