Five Australian soldiers have been killed by Afghan trainees in two separate incidents on Wednesday and Thursday, in the latest of such “insider attacks” leaving a bad taste in the mouth of US officials seeking to finish out a lost war for another two years.

The number of such incidents, termed “green-on-blue” attacks have been increasing steadily as of late, with 35 of them so far this year, ending with 47 NATO members killed, mostly Americans.

The fact that all those killed in the last two incidents were Australian strains an already tense US relationship with Australia over the war in Afghanistan. In April, Australian Prime Minister Julia Gillard announced an early withdrawal to be completed a year before the Obama administration’s so-called withdrawal date at the end of 2014.

Gillard said the loss of the five military personnel the single worst day for her country in war since the Vietnam conflict.

The failure of the US mission in Afghanistan – to build up and train a centralized state and security apparatus – is illustrated clearly in the constant killing of US soldiers by their Afghan counterparts. Much of the security force has been infiltrated by the Taliban or Pakistani agents.

Earlier this month it was reported that the Taliban’s supreme leader Mullah Omar issued a statement bragging about extensive insurgent infiltration in America’s trained security personnel in Afghanistan.

“They are able to (safely) enter bases, offices and intelligence centers of the enemy,” he said. “Then, they easily carry out decisive and coordinated attacks, inflicting heavy losses on the enemy.”

As a former US official told Dexter Filkins of the New Yorker, “several hundred soldiers in the Afghan Army are thought to be agents for the Taliban or for Pakistan.” He said that many insurgents who have infiltrated the Afghan forces and killed US troops “had been planted in the Army by the Taliban or by Inter-Services Intelligence, Pakistan’s main intelligence branch.”

The US mission in Afghanistan has failed miserably. President Obama’s supposed justification for building up Afghan security forces is so they serve as a bulwark against a return to Taliban rule. But the Taliban have seeped deep into those forces the US is spending billions of dollars on training, and the insurgency is as strong as ever.