Ethiopian troops shot at and detained UN staff after they drove through check-points in the conflict-hit northern Tigray region, government spokesman Redwan Hussein has confirmed.
The UN team ignored instructions not to be in the area, he added.
Government forces have been battling the Tigray People’s Liberation Front (TPLF) in the region since 4 November.
The UN team was reportedly trying to visit a camp for Eritrean refugees on Sunday when the shooting occurred.
There has been much concern about the fate of the refugees following unconfirmed reports that Eritrean troops had crossed into Tigray, and had taken some of them back to Eritrea.
Both governments deny that Eritrean troops are in Tigray to help defeat the TPLF.
The UN has appealed to the Ethiopian government to give it “unfettered humanitarian access” to Tigray amid concern about food shortages and medical supplies in a region with a population of more than eight million.
“Some of the UN staff were actually detained and some were shot at,” Mr Redwan was quoted by AFP news agency as saying.
“They broke two check-points to drive to areas where they were not supposed to go, and that they were told not to go. When they were about to break the third one, they were shot at and detained,” he added.
The UN has not yet commented on the incident.
Why are there refugees in Ethiopia?
Many Eritreans have fled across the border to Tigray over the years to escape military conscription and political persecution.
Eritrea is a highly militarised one-party state that has been ruled by President Isaias Afwerki since it gained its independence from Ethiopia in1993.
Ethiopia’s Prime Minister Abiy Ahmed won the Nobel Peace Prize last year for making a deal with Mr Isaias to end the “no war; no peace” situation that had existed between the two countries since their 1998-2000 border war.
Critics say the deal has turned out to be a “security pact” with thousands of Eritrean troops entering Ethiopia to help defeat the TPLF.
Reuters news agency quoted a US government source as confirming that Eritrean forces were in Tigray, despite the denial of the two governments.
“There doesn’t appear to be a doubt anymore,” it quoted the unnamed source as saying.
The TPLF also fired a barrage of rockets into Eritrea after the conflict started.
Is the fighting over?
Ethiopian troops captured Tigray’s capital, Mekelle, from the TPLF on 28 November, but fighting has continued in parts of the region.
“There are a few remnants of the militia or special forces not yet controlled,” Mr Redwan said.
A former guerrilla movement, the TPLF had been the governing party in Tigray since 1991, with about 250,000 fighters under its control.
Mr Abiy ordered the military to oust it from power after it attacked a federal military base in Tigray.
It followed sharp political differences over reforms that Mr Abiy had introduced since taking office in 2018.
More than 40,000 people have fled across the border to Sudan and many others may have been forced from their homes.