Two helicopters are reported to have arrived in a village in Tigray, with senior Eritrean and Ethiopian officers.
The village at which they landed is called Miraqk between Samre and Sokotta.
General Berhanu Jula, Chief of General Staff of Ethiopia, is reported to be on the mission, together with senior Eritrean officers.
Seven foreigners, said to be Europeans, rather than Arabs, are reported to be with them.
They remained in the location all day, with three of the foreigners then leaving, but four remaining.
Local people say they do not know what they are doing, but say the foreigners appear to be military experts.
They may be monitoring Tigrayan military movements, using satellite imaging and other equipment to scan the area.