Saudi Arabia's embassy in Ethiopia called on its citizens in the country to leave immediately on Friday.
The warning came after several groups including the Tigray People's Liberation Front, locked in a year-long conflict with the government, and the Oromo Liberation Army announced a new alliance.
The TPLF said Wednesday that its fighters had reached the town of Kemissie in the Amhara region, 325 kilometres northeast of the capital Addis Ababa, and were running "joint operations" with the OLA, which predicted Addis Ababa could fall in a matter of weeks.
The embassy asked Saudi citizens to leave "in light of the current circumstances" in Ethiopia.
The Saudi ambassador to the country also called on citizens to take all precaution and be wary.
Citizens were urged to contact the embassy in the case of an emergency.
