"We are deeply concerned about this, from top to bottom," Obama told a White House news conference. But he said the best approach, with the fewest number of deaths in the long run, would be to stick to the plan for shifting security responsibilities to the Afghans.
"We are transitioning to Afghan security, and for us to train them effectively we are in much closer contact — our troops are in much closer contact with Afghan troops on an ongoing basis," Obama said. "Part of what we've got to do is to make sure that this model works but it doesn't make our guys more vulnerable."
That vulnerability, however, has been exposed in a strikingly deadly way in recent days.
U.S. officials offer two main theories for why Afghan security forces are turning their weapons on Western partners: infiltration by the Taliban and a U.S.-Afghan culture clash.
Both of those root causes suggest that the problem may get worse as American and other coalition forces shift further into an adviser/mentor role. And that, in turn, raises questions about U.S. ability to train and shape the Afghans into a force that can stand up to the Taliban insurgency after foreign forces end their combat role in 2014.
Jacqueline L. Hazelton, a visiting assistant professor at the University of Rochester, who has extensively studied counterinsurgency strategy, sees the attacks stemming from a combination of Afghan resistance and resentment.
"As disturbing as the attacks are as a Taliban tactic, the broader popular anger revealed — among those the mission is supposed to be most closely allied with and most directly useful to — is even more dangerous for the longer term and reveals a greater rot within," Hazelton said in an email exchange.
As recently as last week, Defense Secretary Leon Panetta called such attacks "sporadic" and a sign of Taliban desperation. But as the assaults continued through the week, he consulted with his top commander in Kabul and then on Saturday called Afghan President Hamid Karzai to express concern. Obama said Monday he would do the same.
"We've got to make sure we're on top of this," Obama said. Obama's Republican election rival, Mitt Romney, said Monday in New Hampshire that the U.S. goal ought to be to "transition from our military to their military as soon as possible," in a way that prevents Afghanistan from collapsing and reverting to being a launching pad for terrorist attacks on the U.S.
Obama said he discussed the problem Monday with the chairman of the Joint Chiefs of Staff, Army Gen. Martin Dempsey, who was already in Kabul to talk to American and Afghan officials about how to halt the killings.
Dempsey said upon his arrival in Kabul that it was important for Karzai and other top government officials to publicly denounce the insider killings, according a Pentagon account of his remarks.
Dempsey also said efforts that began a year ago to improve the vetting of Afghan recruits have yet to solve the problem.
Olga Oliker, an analyst at the Rand Corp. who studies Afghan security forces, said the checks are inevitably spotty, which makes training even more difficult.
"It's Afghanistan," she said. "You just don't have the kinds of records that will give you a strong confidence in a vetting process." And as long as the threat persists it will affect the U.S. training mission, she said.
"If our training efforts take a step back, if our folks are not comfortable genuinely partnering with the Afghans, we'll have even less insight into what they can do," she said Monday. "We'll have even less awareness of when it's appropriate to leave, and we'll be playing even more of a craps game when we withdraw than we are now."
Most U.S. combat troops are scheduled to leave Afghanistan by the end of 2014.
Panetta's spokesman, George Little, described him as "deeply disturbed" by the attacks, including the latest on Sunday in which a U.S. soldier was shot to death when two Afghan police officers suddenly opened fire inside a police station in southern Kandahar province. The victim was a member of a U.S. military advisory team that had been working with the Afghan police inside their station in Spin Boldak district.
Those advisory teams are growing in number and importance to the U.S. strategy for getting Afghan soldiers and police prepared to take over the fight against the insurgency.
For months U.S. officials have emphasized that insider attacks are rarely perpetrated by Taliban infiltrators. Rather, the killings are usually the work of Afghan troops who hold a grudge against their U.S. or allied partner. The intended implication of that analysis is that the problem could be managed by more closely checking the backgrounds and personal circumstances of Afghans who are recruited into the police and army.
Either way, analysts say the willingness of even a small fraction of Afghan forces to turn on their partners is troubling.
Asked about the problem in an Associated Press interview a week ago, Panetta cast it as a sign of the Taliban's desperation, and he said he had been assured by U.S. commanders that the attacks were only "sporadic."
The next day, however, Panetta told a Pentagon news conference that he had conferred with Marine Gen. John Allen, the top U.S. commander in Afghanistan, and discussed with him a variety of measures designed to stem the attacks. These include stepping up counterintelligence efforts to identify potential attackers before they strike.
As of last week U.S. troops in Afghanistan are under orders to carry loaded weapons at all times, even when on their bases, to enable them to respond more quickly if they spot an Afghan soldier preparing to attack them.
The issue has drawn little attention in Congress, although Rep. Frank Wolf, R-Va., last week challenged Dempsey's assertion that Afghan security forces are making progress toward fending for themselves.
"With all due respect," Wolf wrote in a letter last week to Panetta, citing Dempsey's assertion, "how can you state that Afghan security forces are making 'steady progress' when they continue to gun down our forces?"