A hand grenade was thrown Friday at a mosque in the Ethiopian capital of Addis Ababa, wounding at least six people, police said.
Authorities said the explosion went off just after evening prayers at Anwar Mosque in the city's Mercato district, a predominately Muslim neighborhood.
No one immediately claimed responsibility for the attack, and officials said they were trying to determine who was behind it.
Ethiopia has largely avoided attacks by al-Shabab Islamist militants, despite deploying troops to Somalia to fight the radical group.
Kenya, Uganda and Djibouti have all been attacked by the group in retaliation for participating in an African Union force in Somalia.
Ethiopian forces invaded Somalia in 2006 to fight al-Shabab and are still in the country, working in conjunction with AU troops. Those troops have made significant gains, but the militant group remains one of the biggest security threats to the East African region.
Ethiopia's military is considered to be one of the stronger forces in the region.
In 2013, a bomb exploded inside a house in central Addis Ababa. It is believed the attackers were preparing it for an attack at a large football match that was taking place that day.