Reports of an air strike on Mekele came just days after ground fighting resumed between government forces and rebels after a five-month lull, ending a truce and dashing hopes of peace talks.

The Tigray People's Liberation Front (TPLF) said a residential area and a kindergarten were struck in the first air strike on the rebel-held territory in many months.

"Civilians are dead and injured" and a rescue operation was under way, Kindeya Gebrehiwot, a TPLF spokesman, told AFP in a message.

Two humanitarian sources in Ethiopia told AFP they had been notified of an air strike in Mekele, but no details about targets or casualties were immediately available.

Shortly after reports of the strike emerged, the government announced it would "take action" against the TPLF and warned civilians to stay away from military targets in the northern region.

"While the readiness of the federal government to talk unconditionally is preserved, it will take action targeting the military forces... of the TPLF," the Government Communication Service said in a statement.

- International alarm -

A truce in March paused the worst of the bloodshed and allowed aid convoys to return slowly to Tigray, where the UN says millions are severely hungry, and fuel and medicine are in short supply.

But on Wednesday, the warring sides announced a return to the battlefield, with both accusing the other of firing first as fresh offensives erupted along Tigray's southern border.

Details remain unclear, but it appears the fighting has not spread outside an area bordering Tigray, Amhara and Afar.

The return to combat has alarmed the international community, which has been pushing both sides to peacefully resolve the brutal 21-month war in Africa's second most populous nation.

Since the end of June, Abiy's government and the rebels have repeatedly stated their willingness to enter peace negotiations, but disagreed on the terms of such talks.

In recent weeks, too, they have accused each other of making preparations for a return to battle.

Prime Minister Abiy Ahmed sent troops into Tigray in November 2020 to topple the TPLF, accusing the region's former ruling party of orchestrating attacks on federal army camps.

The confrontation followed months of rising tensions between Addis Ababa and the TPLF, which dominated Ethiopian politics for three decades until Abiy took office in 2018.