Forces from Ethiopia's northern region of Tigray said they had shot down a military plane and retaken a town from federal forces on Sunday, as war dragged on a day after the government announced its military offensive was over.

Prime Minister Abiy Ahmed, who has rebuffed international offers to mediate, said on Saturday evening that federal troops had taken control of the Tigrayan capital Mekelle, allaying fears of protracted fighting in the city of 500,000 people. He said federal police would try to arrest the Tigray People's Liberation Front (TPLF) "criminals" and bring them to court.

Police then issued arrest warrants for 17 military officers on charges of treason and embezzlement of public properties, Ethiopian state-affiliated Fana TV reported. Arrest warrants already exist for 117 other senior officers with alleged ties to the TPLF.

TPLF chairman Debretsion Gebremichael said on Saturday that while the group was withdrawing from around the city it would fight on – a declaration that raised the specter of a drawn-out guerrilla war.

"This is about defending our right to self determination," said Debretsion, adding that his forces had shot down an Ethiopian military plane and captured the pilot, and had also retaken the town of Axum.

Rights investigators and civilians fleeing the conflict say fighters from both sides, including civilian militias supporting more formal security forces, have carried out mass killings. Both the government and the TPLF deny their forces were involved.

Lieutenant General Bacha Debele told Fana TV that the military was engaged in "stabilization activities" on Sunday, including assisting people displaced by the fighting to return to their villages.

The International Committee of the Red Cross said that hospitals were running low on supplies such as gloves to care for the wounded, and one hospital lacked body bags for the dead.

Experts have said that a quick military victory in Mekelle might not mark the end of the conflict.

"Although it's not clear how depleted Tigrayan security forces are by the conflict, armed resistance to federal rule may well be backed by much of the regional government and party apparatus, including local militia, as well as by other Tigrayan nationalist elements," said Will Davison, a senior analyst on Ethiopia at the International Crisis Group think tank.

(With input from Reuters)