General Abdel Fattah al-Burhan, who heads the armed forces and the Sovereign Council, Sudan's highest executive body, "has arrived in Gedaref for a security visit", the source said.

There were no further details.

On Wednesday, the army issued a statement saying a unit of Sudanese armed forces had been hit by "an ambush by Ethiopian forces and militias inside Sudanese territories".

It said the attack took place Tuesday evening after "conducting a sweep operation around the Jabal Abutiur region".

There were "casualties and damage" during the ambush, the statement added.

Sudanese media on Thursday said four soldiers were killed and 12 others wounded in the ambush, but the report was not confirmed by the army.

Ethiopia sought to downplay the importance of the incident, and stressed that any problem between the two countries would be resolved through diplomacy.

A foreign ministry spokesman in Addis Ababa told AFP Ethiopian security forces had "repelled a group of (Sudanese) low-ranking officers and farmers, who had encroached on Ethiopian territory".

The incident "should have been resolved through diplomatic channels", the spokesman added, without saying if there had been any casualties.

Ethiopian Prime Minister Abiy Ahmed tweeted that the incident should not damage "historic" ties between his country and Sudan.

"The government is closely following the incident with local militia on the Ethio-Sudan border," he wrote.

"Such incidents will not break the bond between our two countries as we always use dialogue to resolve issues. Those fanning discord clearly do not understand the strength of our historical ties."

Sudan has been flooded by an influx of Ethiopian refugees fleeing a conflict in the northern Tigray region that broke out last month.

Last week, Sudanese Prime Minister Abdalla Hamdok said he had agreed with Abiy in Addis Ababa to hold an urgent meeting of a bloc of east African countries to resolve the crisis.

Fighting has raged since Abiy launched military operations in November targeting Tigray's ruling party, the Tigray People's Liberation Front (TPLF).

Thousands have been killed since the start of the conflict, according to the International Crisis Group, and just over 50,000 people have fled to neighbouring Sudan.