Fierce fighting has erupted in northern Ethiopia between government and regional Tigrayan forces, breaking a five-month-old humanitarian truce.
The truce was agreed to allow aid to enter the region of Tigray - where thousands have died in a brutal civil war and millions need basic supplies.
People in a nearby town told the BBC they had heard heavy weapons firing and seen federal army units arriving.
Both sides have blamed each other for the resurgence in fighting.
On Wednesday morning, Getachew Reda, an adviser to the Tigrayan leader, said Ethiopian forces were responsible for launching an offensive against Tigray after a "week-long provocation" in the neighbouring Amhara region.
Later, the government accused Tigrayan forces of breaking the truce - and said federal army and security forces were responding to their attacks "successfully".
Ethiopian officials also said their forces had shot down a plane carrying weapons for Tigray's military - which was denied by Mr Getachew.
UN chief António Guterres said he was deeply shocked by the fighting and called for an "immediate cessation of hostilities".
A man in Kobo, some 25km (15 miles) from areas where fighting has been reported, told the BBC he heard gunfire starting on Tuesday night.
"At around 5am, the gunshots increased from both sides and we were hearing heavy weapons being fired," he said.
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The Tigray war broke out in Ethiopia's northernmost region in November 2020 - later spreading south to the Amhara and Afar regions.
Thousands died, over two million people fled their homes and the region was hit by an internet and telephone blackout.
The Ethiopian government was accused of imposing a blockade on the region which impeded crucial aid deliveries - which it blamed on Tigrayan forces.
The humanitarian ceasefire achieved in March 2022 resulted in an increase of the amount of aid reaching Tigray.
Active fighting stopped and peace talks seemed imminent.
But now that fighting is back, relief agencies may again find it difficult to reach people in need, and political negotiations may face a setback.