A top-ranking member of Ethiopia's army confirmed that troops from neighbouring Eritrea entered the northern Tigray region during the conflict there, in a video seen by AFP on Wednesday.
Ethiopia's federal government has long denied persistent claims that Eritrean troops were in Tigray, where Prime Minister Abiy Ahmed launched a military offensive against dissident regional leaders in November that left thousands dead.
But Major General Belay Seyoum, the head of the Ethiopian army's northern division, went against those denials in a video dated from the end of December that emerged on social media Wednesday.
"An unwanted foreign force entered into our territory" during the fighting in Tigray, he said in the video, in which he spoke with residents of the regional capital Mekele.
We can solve our problem by ourselves.
Eritrea's army "entered our territory by itself, this has to be made clear," he added, without specifying when the soldiers crossed the border, where they went, or whether they were still in Ethiopia.
"The main mission of the Ethiopia Defense Force is safeguarding the territorial integrity of Ethiopia," he said.
"My conscience doesn't allow me to ask the Eritrean army to help us. We can solve our problem by ourselves."
In December the US State Department said it was "aware of credible reports of Eritrean military involvement in Tigray," and called for the troops to be withdrawn.
Ethiopia's ambassador to the US Fitsum Arega denied the claim, tweeting: "Repeat a lie often enough and it becomes the truth!".
Tigray residents also told AFP that Eritrean troops were in the region, accusing them of various abuses and looting.
Prime Minister Abiy reached a historic peace agreement with Eritrea shortly after taking office in 2018, winning him the 2019 Nobel Peace Prize.
Abiy's ascension ended decades of federal political dominance by the Tigray People's Liberation Front (TPLF), sworn enemies of Eritrean President Isaias Afwerki after a 1998-2000 war between the two countries.
The premier launched the military operation against Tigray's TPLF leaders on November 4, claiming victory when federal forces captured Mekele later that month.
Before the conflict began, Tigray was home to 96,000 Eritrean refugees who fled Afwerki's regime in one of the world's most authoritarian states.
The UN is among those to have expressed fear the Eritrean refugees in Tigray could face reprisals from Eritrean troops, or even be forced to return to the country.
Also on Wednesday, the council representing Ethiopia's Muslims condemned the partial destruction of one of Africa's oldest mosques in the Tigray fighting.
Qassim Mohammed Tajuddin, the secretary of the Ethiopia Islamic Affairs Supreme Council, said the al-Nejashi Mosque had been hit by artillery fire and its materials had been looted.
He called on the government "to bring to justice speedily those entities that committed these shameful acts".
Built in the 7th century, the mosque is considered one of the oldest Muslim burial sites. Muslims believe it houses the tomb of several of Prophet Mohammed's disciples.