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… after the United States has spent almost $300 billion on the war in Afghanistan, the Taliban are stronger than at any time since 2001

A Taliban fighter loyal to Jalaluddin Haqqani

Wikileaks documents suggest that incidences of the Taliban firing on US aircraft have been suppressed from public record. Photograph: Ghaith Abdul-AhadThe legendary ability of small, shoulder-born missile launchers to transform the fortunes of otherwise crudely armed insurgents is one of the most alarming threats to emerge from the Wikileaks archive.

Soviet troops discovered in 1986 when the CIA decided to put heat-seeking Stinger missiles into the hands of the otherwise low-tech Afghan resistance, such weapons can make life impossible for modern armies.

A US soldier checks machine-gun sights at an outpost near Camp Tillman, Afghanistan, in October 2006 after rockets were fired into the base near the Pakistan border. Photograph: John Moore/Getty Images

As depicted in the Tom Hank’s film Charlie Wilson’s War, bearded warriors were able to stand on hilltops and blast the dreaded Russian attack helicopters out of the sky, ultimately forcing them to fly far higher, to much less effect.

That image still haunts Nato commanders who are all too aware of how much they rely on thousands of transport planes, helicopters and drone surveillance craft to kill insurgents from the air and move troops around an increasingly hostile theatre of war.

It has long been the international coalition’s claim that whilst the Taliban might try to acquire technology capable of shooting down aircraft they had failed to do so, and were unlikely to ever succeed.

Nonetheless, the risk is taken extremely seriously and the sight of distraction flares blasting out of the side of military helicopters are a regular sight in the skies above Afghanistan. The countermeasures, designed to confuse the heat seeking cone of the missile, are so sensitively calibrated they can be easily set off by a false alarm. But according to the WikiLeaks documents, there have been several cases of insurgents firing on US aircraft, all of which have been suppressed from the public record.

TIC, RPG: glossary of military terms for incidents like this, where an Afghan Army soldier fires a rocket propelled grenade at suspected Taliban at combat outpost Nolen, north of Kandahar. Photograph: Bob Strong/Reuters

In May 2007 a US Chinook was hit by a missile in Helmand after it had departed from the Kajaki base in the north of the province, killing everyone on board, although the US claimed it had been downed by lucky shot from a rocket propelled grenade (RPG) which has no heat seeking capability.

The previous month the crew of a British Chinook had reported a missile flying 50ft past the aircraft before exploding. In July 2007, the crew of a C-130 transport plane reported that they had seen a rocket fly past them whilst they were refuelling at 11,000 feet. That event was actually reported by British journalist Tom Coghlan who quoted a military spokesman who said any such incidents were classified and could not be commented on.

An official at HQ ISAF said he too was unable to comment on any incident involving anti-aircraft missiles.

It is not clear why the coalition is so reluctant to publicly admit the risks posed to coalition aircraft by missiles.

British defence officials said there was no evidence of weapons bigger than RPGs being fired at helicopters, but insurgents are making greater efforts to shoot down helicopters, which they believe have great propaganda value for them.

“There is much greater focus on carefully coordinated attacks on helicopters by RPGs [rocket propelled grenades] or small arms”, a Ministry of Defence source said. The insurgents “are constantly watching us and adapting their tactics”, said a senior military official.

The Afghan war logs reveal the difficulties encountered by US troops when they tried to talk to villagers. Photograph: John Moore/Getty Images

In the latest incident an American Cobra helicopter was shot at in Marjah in central Helmand province, sources told the Guardian.

David Cameron was forced last month to abandon a visit to British troops in Helmand province after an intelligence report suggested the Taliban was plotting to target an unnamed VIP. The prime minister’s Chinook helicopter diverted after five minutes in the air when the information was received.

Until very recently intelligence officials have argued that there was little risk that heat-seeking missiles ever be acquired by the Taliban, although the released military intelligence includes numerous reports of insurgent groups in individual provinces who were thought to have the capability as early as 2005.

A western diplomat recently told the Guardian that the Taliban could not access such weapons because they are not freely available on the black market run by the world’s private arms dealers.

Taliban fighters in the a madrasa near the northern city of Kundoz, Afghanistan. Photograph: Ghaith Abdul-Ahad for the Guardian

Another obvious source would be foreign government’s hostile to the US occupation in Afghanistan, with perhaps the most likely source being neighbouring Iran.

According to one unconfirmed April 1 2004 intelligence report, seven anti-aircraft missiles, originally acquired in Algeria, were sneaked over the porous Afghan border.

But one intelligence source told the Guardian that although Shia Iran is happy to provide limited support to insurgents, it would never want to see such weapons in the hands of a Sunni movement which it nearly went to war with in 1998 when the Taliban killed ten Iranian diplomats.

Another possibility is that the missiles were rare leftovers from the original stock of some 2,000-2,500 Stingers distributed to the mujahideen by the CIA.

Even though the missile launchers are unlikely to work because their batteries degrade over time, the CIA made a big effort in the 1990s trying to recover as many Stingers as possible, offering between $80,000 and $150,000 per weapon in a buyback programme.