Citing a 60 percent decline in violence in Iraq over the last six months, Gen. David Petraeus said Thursday that maintaining security is easier than establishing it and gives him more flexibility in deploying forces.

Armed with charts showing that as of Wednesday, weekly attacks and Iraqi civilian deaths have plunged to levels not seen here since early 2006, Petraeus said the reduction lets him make force adjustments to address remaining problem areas, which would include northern Iraq.

Speaking to reporters at the U.S. military's Camp Victory, he said the improved security is due to a number of factors including a "a reduction in some of the signature attacks that are associated with weapons provided by Iran," as well as a cease-fire called by radical Shiite cleric Muqtada al-Sadr that he said had a particularly noticeable impact what had been one of the most violent areas of Baghdad.

And he said there has been a "reduction in some of the signature attacks" associated with insurgents using Iranian weapons, including deadly armor-piercing rounds.

But, he added, that it is "hard to tell if that's because there has already been a cessation of provision of those items, or if there has been direction to stop."

At the same time, he said the military has detained individuals as recently as October who were trained by Iranians, evidence that the instruction has continued.

Petreaus, who is scheduled to give Congress and the American people an update next March on progress in Iraq, and map out some plans for U.S. force levels down the road, refused to offer too much optimism.

"Nobody says anything about turning a corner, seeing lights at the end of tunnels, any of those other phrases," said Petraeus. "You just keep your head down and keep moving."

He said that around Thanksgiving commanders looked back at violence levels a year ago, and six months ago, and found a declining line in which violence had declined from a time when hundreds of Iraqis were killed and injured and US troops took heavy losses in a number of horrific attacks, to a time of still somewhat steady but less deadly attacks, to a day last month when there were just 45-50 attacks.

Petraeus met for about an hour Thursday with Defense Secretary Robert Gates, who was in Iraq for his sixth visit in the past year.

The general has overseen the military's build up in Iraq this year, as force levels jumped to 20 combat brigades, with more than 180,000 troops, during certain times when some of the units overlapped as they moved in and out of the country.

"There's nobody in uniform who is doing victory dances in the end zone," said Petraeus, saying it will require more tough work against a very dangerous adversary.