U.S. combat forces left Iraq in December 2011 according to the terms outlined in a status of forces agreement. A quarterly report by U.S. Special Inspector General for Iraq Reconstruction Stuart Bowen said the number of violent attacks in Iraq is up to levels not seen in more than two years.
The report said the civil war in neighboring Syria was contributing to regional instability.
"Domestic security also has declined amid regular reports of a reviving al-Qaida in Iraq," the report stated. "Overall in Iraq, violence this quarter was the worst in two years."
A report from Bloomberg News cites U.S. officials, speaking on condition of anonymity, who said there were fewer than 800 fighters loyal to al-Qaida when U.S. forces left at the end of 2011.
Bowen said Iraqi Deputy Prime Minister of Interior Adnan al-Asadi said groups like al-Qaida in Iraq were gaining strength, however, because the country lacked the intelligence capabilities to detect and prevent attacks organized by militant groups.
It's been "a troubled year" in Iraq, the inspector general said in the report.