Fighting over disputed land along borders of Ethiopia’s Tigray and Amhara regions has displaced close to 29,000 people, the United Nations says.
Fighting began last week between forces from the two regions in Raya Alamata district, which is claimed by both.
Officials in Amhara have accused forces from Tigray of launching an invasion, but former rebels in Tigray deny this.
A two-year civil war ended in late 2022 in Ethiopia, after central government signed a peace deal with Tigray forces.
However, issues of contested areas, disarmament of ex-combatants, and the fate of hundreds of thousands of Tigrayans forced out of their homes during the war remain unresolved.
The contested district of Raya Alamata had been under Tigray until war broke out in 2020, but the Amhara forces have since seized it.
Following the resurgence of the latest fighting, Tigray forces have reportedly advanced towards some areas in the district.
Life-saving assistance is urgently required, the UN said, adding that some families were sheltering in open areas in nearby Amhara districts of Kobo and Sekota.
Meanwhile the embassies of seven Western countries – including the US and the UK – have released a joint statement expressing their concern at the reported violence.
They are calling for de-escalation and have encouraged disarmament and demobilisation.