The Tigray People's Liberation Front, the party that controls most of the northern Ethiopia region of Tigray, has accused Eritrea of attacking its troops.
In another development in the conflict, aid organisations suspended their operations in an area of northwest Tigray where 56 civilians were killed by an air strike over the weekend, the UN agency for humanitarian affairs (UNOCHA) said.
"The Eritrean military launched fresh attacks against our forces yesterday in Sigem Kofolo ... located in Northwestern Tigray close to Sheraro town," TPLF spokesman Getachew Reda wrote on Twitter on Sunday.
Reuters could not verify the alleged attack as the communication network is down in the area.
Eritrean Information Minister Yemane Gebremeskel did not immediately respond to requests for comment.
Ethiopia's military spokesman Colonel Getnet Adane and government spokesman Legesse Tulu did not immediately respond to requests for comment. Prime Minister Abiy Ahmed's spokeswoman Billene Seyoum also did not respond to a request for comment.
A lack of medicines, fuel and other essential commodities was "disrupting the response to the injured," UNOCHA said in a statement announcing suspension of operations following the air strike that hit a camp for internally displaced people late on Friday.
"Humanitarian partners suspended activities in the area due the ongoing threats of drone strikes," the agency told Reuters, without giving further details.
War broke out in the mountainous region of 5 million people 14 months ago, pitting Tigrayan forces against federal troops backed by their Eritrean counterparts.
Eritrean President Isaias Afwerki told the state-run Eri-TV on Saturday that his troops would strive to prevent Tigrayan forces from attacking his country, or threatening the stability of Ethiopia.
Eritrean forces have fought against Tigrayan forces since the start of the war in support of Abiy's troops, but both nations spent the first five months of the conflict denying the Eritrean presence.
The Eritrean troops withdrew from most of the region in June, the same month that Ethiopian federal troops also withdrew.
Last month, Tigrayan forces withdrew from neighbouring regions they had invaded in July, in a step toward a potential ceasefire.
Reuters has reported atrocities by all sides, including Eritrea, which the parties to the fighting have denied.
The conflict in northern Ethiopia has killed thousands of civilians and displaced millions.Â