The decision announced yesterday to cut back on joint operations undertaken by international and Afghan forces raises crucial questions about the key plank of the exit strategy from the 11-year war which has proved costly in lives and money.

The move is also a significant propaganda coup for the insurgents, coming just after their assault on Camp Bastion which resulted in the destruction of warplanes worth $200m. For the British and coalition troops, the announcement in Washington will only highlight the mistrust which has been the inevitable consequence of 51 deaths inflicted by their supposed Afghan brothers-in-arms.

What added to the sense of uncertainty and drift was the way the news of the order filtered out, with allies in the coalition seemingly kept in the dark by the US and Nato high command. The Defence Secretary, Philip Hammond, clearly had not been told about it when he appeared before the Commons on Monday after the latest killings of two British soldiers by an Afghan in uniform.

Neither, perhaps more importantly, had the Afghans. Afzal Amaan, the head of operations at the defence department in Kabul, said yesterday: "We haven't heard officially from the foreign forces about this. It will, of course, have a negative impact on our operations. Right now, foreign forces help us in air support, carrying our personnel, wounded and dead out of the battlefields, in logistics and training."

Major Adam Wojacjk, a spokesman for Isaf (International Security Assistance Force), acknowledged that the "vast majority" of the 350,000-strong Afghan security forces would be affected by the suspension of joint operations for units smaller than battalion strength, where most training takes place. This means, in effect, that Afghan forces will have to undertake missions at a time of a renewed insurgent offensive without support from Nato.

Just how precarious the situation remains was illustrated by the bombing of a minibus carrying foreign workers on Kabul's Airport Road yesterday. The victims included French, South African and Russian nationals, some of them said to be flight crew. A woman driving a Toyota Corolla packed with explosives rammed into the bus, one of the very few occasions when females have carried out such attacks.

The West's exit from the conflict is predicated on Afghan forces taking over control of security by 2014. Mr Hammond declared last week that this was going so well, that the scale of British drawdown may actually be hastened next year.

The Defence Secretary insisted yesterday that the role of UK forces in Helmand would remain "substantially unchallenged" as the commanding officer for the region was happy for British mentoring and partnering to continue at below battalion level. However, Isaf officials in Kabul were adamant that there was no blanket exemption from the order. "The need for each operation will be evaluated on a case-by-case basis", said a senior officer.

Paul Flynn, a Labour MP, was expelled from the Commons for accusing ministers of lying over Afghan policy. "Isn't this very similar to the situation at the end of the First World War, when it was said that politicians lied and soldiers died? The reality was, as it is now, that our brave soldiers – lions – are being led by ministerial donkeys," he stated.

The rush for a withdrawal from Afghanistan has created the conditions to allow the Taliban to infiltrate the local security forces, Afghan and some Western military commanders insist, with around 7,000 recruits for the Afghan police and army having to be processed every month. Since the rise in the "green on blue" attacks, vetting has been tightened up, and one in 35 applicants is said to have been rejected. One Afghan official said 420 out of the 15,000 who applied to join the army in the last seven months appeared to have the sole aim of murdering Western troops.