Ethiopia has launched a major offensive against rebel forces in the Tigray region, carrying out air strikes in its latest bid to gain the upper hand in an almost yearlong civil war.

The move from the government of Prime Minister Abiy Ahmed comes days after he was inaugurated for a new five-year term as leader of Africa’s second-most populous country, and amid threats that the U.S. may impose sanctions against individuals and entities responsible for the violence.

Getachew Reda, a senior member of the Tigray People’s Liberation Front, said air strikes and artillery bombardment had struck Tigray in the past two days. The extent of any casualties was unclear.

In June, Liberation Front forces recaptured their capital Mekelle from Ethiopian troops and allied fighters from Eritrea.

“At this stage it is mostly air, drone and artillery bombardment,” Getachew said via text message. He added that thousands of pro-government combatants had been spotted near the towns of Hara, Wergesa and Wegel Tena close to the Tigray border in Ethiopia’s northern Amhara region.

“We will maintain our defensive positions. We are confident we will thwart the offensive on all fronts,” he said.

Getachew’s comments on the state of the combat couldn’t be independently verified. Billene Seyoum, a spokeswoman for Abiy, didn’t respond to questions.

The latest military buildup is taking place in the areas where Abiy’s forces were present in the early days of the conflict. For months, forces loyal to Abiy and soldiers from Eritrea were accused of carrying out grievous crimes including rape and the massacre of civilians.

The conflict began in November when Abiy ordered an incursion in retaliation for an attack on an army base. The United Nations has warned that more than 400,000 people in the region are on the brink of famine.

The Biden administration this week called a CNN report that Ethiopian Airlines Group used a commercial airline to ferry arms to Eritrea a grave allegation, and said Ethiopia could be hit with sanctions if conflict in the Tigray region persists. The carrier denied it had done so.

Earlier this month, Ethiopia ordered seven senior UN staff members to leave the country for allegedly meddling in its internal affairs, a move condemned by UN and U.S. officials.