At the same time, the seizure of enemy weapons more than doubled as a higher number of improvised explosive devices were found before they exploded, USA Today reported Tuesday.
IEDs are the single greatest cause of casualties among U.S. troops.
Preliminary data for August indicates a decline of at least 100 in IEDs planted, said Navy Lt. Cmdr. Kaye Sweetser, a military spokeswoman.
"This is an indication that the Afghan locals are starting to be fed up with the insurgents and decreasing any support of them," she said.
Military analyst Michael O'Hanlon of the Brookings Institution said the large number of bombs indicates the insurgency is well-supplied and not giving up.
"The IED numbers remain higher than predicted. That doesn't mean the strategy is a failure, but it does mean we face a very resilient, well-supplied insurgency," O'Hanlon said.