The slaying Thursday night of three members of a US Marines special operations unit by a uniformed commander in the US-backed security forces brought to eight the number of Americans killed this week in Afghanistan.

Friday’s killings also marked the third attack on US-led occupation forces by their supposed Afghan allies in a week. These “green-on-blue” attacks, as they are dubbed by the Pentagon and NATO, have escalated sharply as Washington attempts to implement its strategy for continuing US domination of the country after the end of 2014, when all American “combat forces” are supposed to be withdrawn from the country.

This is based principally on training Afghan puppet army and police forces to conduct counterinsurgency operations, albeit with the continued deployment of tens of thousands US “trainers” and special forces units, long after the 2014 deadline.

Friday’s attack took place in the southern province of Helmand, a focus of US operations since the “surge” of 30,000 additional troops into Afghanistan ordered by Obama in December 2009.

As in virtually all such attacks, the US military reported that the shooting was the work of an “individual wearing an Afghan uniform,” suggesting that it could have been the work of an Afghan masquerading as a soldier or policeman.

Afghan officials, however, identified the shooter as Asadullah, the commander of a unit of the Afghan Local Police (ALP). He had reportedly invited the Marines to dinner to discuss security in the Sarwan Qala neighborhood in Helmand’s Sangin district. Once they arrived, he—and several police recruits, according to some reports—stood up and shot them dead.

The ALP has been set up and funded by the occupation forces to function as a local defense force and is seen as key to US strategy. It has been the subject of intense controversy, with the US-backed government of President Hamid Karzai first opposing it as an armed unit outside its control. There have been numerous charges of extra-judicial killings, torture, rape, extortion and other human rights abuses against the ALP, and indications that it frequently functions as the militia of corrupt local warlords.

The Taliban claimed responsibility for the killings, reporting that the police commander had joined their fighters after fleeing the scene of the shootings.

The third attack on US and NATO forces in Afghanistan by Afghan puppet forces this week, the killing of the Marines in Helmand follows an incident two days earlier in eastern Laghman province, where an Afghan National Army soldier turned his gun on NATO troops, wounding several before being killed by return fire.

Also on August 7, two Afghan soldiers opened fire and killed a US soldier and wounded four others in eastern Paktia province before being detained.

So far this year, 34 US and other occupation troops have been killed in at least 25 such attacks. This compares to a total of 35 killed for all of 2011 in at least 21 attacks. The real number of these attacks is undoubtedly far greater, as the Pentagon rarely reports incidents unless there are American or NATO fatalities.

Washington has attempted to dismiss the significance of this steady escalation of killings of American soldiers by members of supposedly allied Afghan forces, a phenomenon that the US military has never before faced in its history.

A July report issued by the Pentagon claimed that “green on blue” attacks were not the result of infiltration of the Afghan forces by the Taliban, or indeed the hostility of the Afghan people to over a decade of US occupation of their country, but were merely “due to isolated personal grievances against coalition personnel.”

This view was echoed Friday by Brig. Gen. Gunter Katz, a spokesman for the US-led occupation. Calling the shootings an “isolated incident,” the general said the attack was “tragic, but doesn't reflect the security situation.”

Similarly, White House spokesman Jay Carney dismissed the attacks, saying that their “operational impact has been negligible.”

In March, Gen. John Allen, the top US commander was a bit more frank, acknowledging that the attacks had led to an “erosion of trust,” an understatement that points to the deeply corrosive effect on the morale of US and other foreign occupation troops as they face the continuing threat of being killed by those they are supposed to be training.

Measures taken to counter these attacks—more vetting of Afghan recruits and the deployment of US soldiers to act as “guardian angels” of the trainers, protecting them against their pupils—have seemingly had little impact.

The effects of the training have fallen far behind what Washington requires to field an effective puppet force, with just 7 percent of the Afghan National Army units and 9 percent of police units rated at the highest level of effectiveness. Not even these units are capable of operating without extensive US support in terms of air power, logistics and “advisers.” The US military itself acknowledges that Afghan forces are plagued by rampant corruption and ethnic divisions. Pashtuns, Afghanistan’s largest ethnic group—comprising over 40 percent of the population—and the main base of support for the Taliban, have comprised barely 6 percent of recruits to the Afghan security forces.

Attacks by armed groups opposing the occupation continue to mount, increasing to 110 a day during the three months ending in June. For all of President Obama’s claims that his surge succeeded in breaking the momentum of the Taliban, that momentum appears only to be growing.

In the latest devastating attack, insurgents struck at the command staff of the 4th Brigade Combat Team of the 4th Infantry Division in Asadabad, the capital of Kunar Province, which borders on Pakistan and has been the scene of some of the most intense fighting in the nearly 11-year-old US war.

Two insurgents walked up to a group of officers as they entered their compound Wednesday, detonating explosive vests. Killed in the suicide attack were two majors, and an Army command sergeant major, the most senior enlisted man in the unit. Also killed was the US Agency for International Development representative in the area and an Afghan interpreter. A number of other personnel were seriously wounded. Initial reports included among these the unit’s commanding colonel, but a spokesman for the occupation later denied this.

Meanwhile, the United Nations Assistance Mission in Afghanistan issued a report this week stating that 1,145 Afghan civilians had been killed and another nearly 2,000 wounded in the first six months of 2012. While this represented a 15 percent drop in civilian casualties compared to what the mission reported last year, UN officials cautioned that this in no way reflected a lessening of the conflict.

“We must remember that Afghan children, women and men continue to be killed at alarmingly high levels,” said Nicholas Haysom, deputy UN special envoy to Afghanistan.

The decline in casualties is likely a result of the harsher winter in Afghanistan this year, which delayed the start of the fighting season. In July, the number of civilian casualties was 5 percent higher than in the same month last year.

On Tuesday, local authorities in Afghanistan’s western Nimroz province reported that several civilians were killed the previous night in a night raid by US special forces troops. According to Pajhwok Afghan News (PAN), Mohammad Hashim, the district chief for Khasrod, said that the victims included two brothers and a couple from two separate families. Several children were also wounded in the attack.