Washington, D.C. ? The U.S. military has captured at least two suspects in the recent spate of helicopter downings in Iraq, the No. 2 American commander there said Thursday.

Army Lt. Gen. Ray Odierno also said the military had noted similarities in some of the eight helicopter incidents in the past month in which aircraft were shot down or landed under fire. A few of them might have been ambushed, he said.

Odierno declined to say what other similarities had been found in tactics and techniques, but said officials were studying them closely to try to better protect the aircraft and capture militants from the cells involved, which he said he believes are “al-Qaida-associated cells.”

Odierno said he didn’t think the spate of downings – and two incidents of chlorine bombs this week – signaled a more capable insurgency.

“What they’re trying to do is … adapt in such ways where they can continue to create instability,” Odierno told Pentagon reporters in a video conference from Baghdad.