Despite a decline in violence in Iraq, Northern Iraq has become more violent than other regions as Al Qaeda and other militants move there to avoid coalition operations elsewhere, the region's top U.S. commander said Monday.

Army Maj. Gen. Mark P. Hertling said Al Qaeda cells still operate in all the key cities in the north.

"What you're seeing is the enemy shifting," he told Pentagon reporters in a video conference from outside Tikrit in northern Iraq.

Hertling said militants have been pushed east to his area from Anbar by the so-called Awakening movement, in which local tribes have allied with the coalition against Al Qaeda. Others have been pushed north to his area from the Baghdad region, where this year's U.S. troop escalation has made more operations possible.

"The attacks are still much higher than I would like here in the north but they are continuing to decrease in numbers and scale of attacks," Hertling said.

He said 1,830 roadside bombs were placed in his region in June, compared with 900 last month.

The U.S. military says overall attacks in Iraq have fallen 55 percent since nearly 30,000 additional American troops arrived in Iraq by June, and some areas are experiencing their lowest levels of violence since the summer of 2005.

Hertling would not say how many Al Qaeda members he believes are in his area, but he said a recently started operation has netted some 200 detainees who are giving officials good information about the organization and how it operates.

"There are certainly cells remaining in all the key cities" in the north, he said. "We're doing our very best on a daily basis to break those cells down," Hertling said. "We've had success but it is still going to be a very tough fight to eliminate those terrorists and insurgents and extremists completely from those areas."

The U.S. military said Sunday that overall violence in Iraq is down 55 percent since a troop buildup began this year.