Eighteen Iranian and three Iraqi pipeline workers were killed in an armed attack by unidentified gunmen in Iraq.

Reports indicate that five Iranians and two Iraqis were also injured in the attack which Iraqi authorities have linked to Al-Qaida although the responsibility for the attack has not been claimed by any groups.

Iran’s foreign ministry has condemned the attack, saying, “The details of this terrorist attack are under investigation.”

In recent months, violence in Iraq has escalated to levels not seen since 2008, and according to official reports, at least 7,150 civilians were killed in Iraq in 2013.