NAIROBI, Kenya (AP) — Ethiopia’s conflict in its powerful Tigray region continues 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 remain 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 challenges efforts to verify the Ethiopian federal government’s account of events.

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, who was 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.