The African Union said previously that the polls took place in a challenging security environment, particularly in parts of Oromia, Amhara and Tigray.
Critics say Ethiopia has never held truly free and fair elections, with those in power during elections always winning by a wide margin.
Since coming to power, Abiy has overseen fast growth thanks largely to a state-led construction boom and surging exports such as coffee.
However, the World Bank says Ethiopia remains dependent on international aid, and that 43 percent of the population lives in poverty.
