NAIROBI, Kenya (AP) — Ethiopia’s conflict in its powerful Tigray region continued Thursday after Prime Minister Abiy Ahmed told the nation the military will carry out further operations this week in response to an alleged deadly attack on a military base by the regional government.

Communications remained cut off in the northern Tigray region after services disappeared at just around the time Abiy’s office first announced the attack and military action early Wednesday. The lack of contact has challenged efforts to verify the Ethiopian federal government’s account of events.

The Tigray capital, Mekele, appeared calm on Thursday morning but skirmishes took place elsewhere, a source told The Associated Press, speaking on condition of anonymity because they were not authorized to speak to the media about it.

“Certainly there is fighting, but I don’t think anyone can credibly assert who attacked who first,” former U.S. diplomat Payton Knopf, a senior advisor with the United States Institute of Peace, told the AP on Wednesday night. He wondered why the well-armed Tigray region's forces would start by raiding a command post: “They’re not lacking for weaponry.”

Observers warn that a civil war in Africa’s second most populous country, involving the heavily armed Tigray region, could destabilize the already turbulent Horn of Africa. The prime minister, awarded the Nobel Peace Prize last year for his sweeping political reforms, now faces his greatest challenge in holding together a country of some 110 million people with multiple ethnic and other grievances.

Aid organizations and human rights groups are pleading for communications links to be restored and warning of a humanitarian disaster if hundreds of thousands of people flee fighting in the midst of the COVID-19 pandemic.

Ethiopia has imposed a six-month state of emergency on the Tigray region, which played a dominant role in the country’s government and military before Abiy took office in 2018. Since then the region, feeling marginalized, has split from the ruling coalition and defied Abiy by holding a regional election in September that the federal government called illegal.

Tigray borders Eritrea, which fought a bloody border war with Ethiopia before the countries made peace in 2018, shortly after Abiy took power. The Tigray regional government, the Tigray People’s Liberation Front, has accused Eritrea of teaming up with Ethiopia's federal government in this week's offensive. Eritrea's information minister did not respond to a request for comment.

TPLF officials in a statement aired on Tigray TV on Wednesday said airspace over the region is closed and any damage to people or property will be met with “proportional” measures. It accused the federal government of deploying troops to “cow the people of Tigray into submission by force."

The TPLF also invited other members of the security forces across Ethiopia to join it in “opposing the colonel Abiy’s regime.”

The head of Ethiopia’s new state of emergency committee, Redwan Hussein, told reporters the federal government’s conflict is with a “small clique of TPLF circles that are keen to destabilize Ethiopia,” and the government must do everything possible to “liberate the Tigrayan people.”

The TPLF over the weekend told the AP it’s not interested in negotiating with the federal government. It was not clear if that stance had changed in light of the new events.

U.S. Secretary of State Mike Pompeo in a statement overnight said the U.S. was “deeply concerned by reports that the Tigray People’s Liberation Front carried out attacks on Ethiopian National Defense Force bases in Ethiopia’s Tigray region on November 3. We are saddened by the tragic loss of life and urge immediate action to restore the peace and de-escalate tensions."