The unidentified assailants attacked the Musab bin Omar mosque in the village in Iraq's Diyala province, northeast of Baghdad. The incident occurred as traditional Friday prayers were being conducted.
Local officials said members of the Islamic State are present in the area, seeking recruits from two prominent Sunni tribes, who thus far have refused to be involved in the militant movement.
Attacks on mosques are common in Iraq, and are typically treated with counter-attacks and revenge killings. The current wave of attacks, and the involvement of IS members, has brought violence in Iraq to the levels of the sectarian civil wars of 2006 and 2007. The nearby towns of Jalula and al-Saadiyah recently fell to IS forces, although Imam Weis remains in government hands.
Fifteen Sunni Muslims were executed in July in nearby Baquba for allegedly providing lists of names of IS militants to Shia forces for purposes of a hit list, police said.