The incident happened at a terrorist training camp north of Baghdad. The person conducting the session was not identified by name by the Iraqi military but was described as a prolific recruiter for the Sunni militant group known as the Islamic State of Iraq and Syria, or ISIS, the New York Times said.
The group has staged uprisings in Anbar province, taking control of Fallujah from the Shiite-controlled Iraqi government.
The Iraqi military said 22 people were killed in the accidental bombing, 15 were wounded and eight others arrested as they tried to flee the area. A cache of explosives and weapons was also recovered from the camp.
In other news, a truck-bomb explosion at an al-Qaida base in heavily Sunni Salahudin province in Iraq killed 25 militants, a police official said.
The official said gunmen were building the bomb when it exploded Sunday in a village near Samarra, China's state-run news agency Xinhua reported Monday.
Several militants were injured in the explosion and removed before Iraqi security forces arrived, the official said.