Marine Gen. John R. Allen, speaking to reporters at the Pentagon from his headquarters in Kabul, said the reasons behind the attacks are not fully understood and likely can be attributed to a variety of factors, including Taliban infiltration of the Afghan security forces.
He cited Ramadan and the requirement for Muslims to not eat or drink during daylight hours as another factor.
"It's a very tough time for these (Afghan) forces," he said, particularly since they were fasting during the heat of the summer and the peak of the fighting season and have been facing combat strains for many years.
"We believe that the combination of many of these particular factors may have come together during the last several weeks to generate the larger numbers" of attacks, he said. Already this month there have been at least 10 "insider" attacks by Afghans, killing 10 Americans. The latest was Sunday when an Afghan police officer opened fire inside a police station in the southern district of Spin Boldak, killing a 55-year-old U.S. Army soldier.
The general said that roughly 25 percent of insider attacks can be linked to the Taliban, who in some cases have impersonated members of the Afghan security forces and in some cases have co-opted them through threats.
Allen was asked about an assertion by the office of President Hamid Karzai on Wednesday that the insider attacks can be blamed on the brainwashing of Afghan recruits by foreign intelligence agents.
"I'm looking forward to Afghanistan providing us with the intelligence that permits them to come to that conclusion so that we can understand how they've drawn that conclusion," Allen said.
Offering an overview of the war effort, Allen said the strategy of handing off security responsibilities to the Afghans is on track.
"It's been a highly successful summer," he said.
"Coalition and Afghan forces have maintained unrelenting pressure on the insurgents, and we have denied and disrupted their operations and have largely pushed them out of the population centers," he said. "We've limited their freedom of movement, and we've interdicted their logistics. We've taken scores of their leaders and fighters off the battlefield, and we've systematically separated the insurgents from more and more of the Afghan population."