The Ketab Jund al-Imam, a Shi’ite militia fighting alongside the Iraqi government against ISIS, was clashing with ISIS forces near Tikrit overnight when it made the mistake of calling for Iraqi government support.

What followed was a drone strike by the Iraqi forces against the militia itself, killing nine of their fighters and wounding 15 others. Iraqi officials have called for an investigation to find out what happened in the incident.

US officials denied any involvement in the incident, after initial reports condemned them for attacking the militias. The Pentagon has said it was an Iraqi drone strike “for sure.” There has been no Iraqi comment suggesting they are contesting that assessment.

The militia was fighting ISIS near the Speicher military base, just northwest of Tikrit. The base is one of several that ISIS has been contesting since the fall of Ramadi in recent weeks, an effort to overcome the high-profile defeat with a new victory of their own.