It is claimed that the missiles have been fitted with new battery packs allegedly provided by the Pakistani intelligence service, ISI, in the past four months.
Western sources say they are not sure whether the supplies, needed to make the US-made missiles operational, were provided by rogue elements within the Pakistani secret service, or approved at a high level.
However, the effect of re-arming the Stingers could be to make Nato aircraft vulnerable while Britain is deployingalmost 6,000 soldiers in southern Afghanistan.
It is believed that the battery packs had been fitted in between 18 and 20 heat-seeking Stingers which can hit targets at around 12,000 feet. They are reported to have been handed over in the Quetta region in Pakistan known to be used by the Taliban to launch attacks in southern Afghanistan.
US and Nato forces have carried out a series of searches along the border areas in the hunt for the missiles, with a large-scale operation a month ago. No British forces were involved. It is not known if Stingers have been recovered.
The Pakistan government yesterday denied the accusation as "baseless". An official spokesman said: "Pakistan has lost more security personnel in the fight against terror than any other country. We make no distinction in this fight between al-Qa'ida and the Taliban. No evidence to the contrary has ever been provided; these are just rumours, unsubstantiated allegations and innuendo."
The Pakistan government also rejected suggestions of involvement by ISI rogue elements. "Our military and security services are disciplined forces," the spokesman said.
Reports that the batteries had been fitted to the missiles surfaced at the end of last year along the border between Afghanistan and Pakistan. It followed efforts by Afghan officials to buy Stingers which had been supplied to the Afghan Mujahedin by the US during the war against the Russians.
Taliban fighters have yet to successfully use anti-aircraft missiles against US and Nato forces. However, both US and British pilots, who fly Tornados from a base in Kandahar, report that ground-to-air missiles have been fired at them.
Western diplomats and military are extremely sensitive about the Stinger allegations as it comes at a time when Afghanistan and Pakistan are engaged in an escalating feud over insurgent attacks in Afghanistan.
The Afghan government claims Pakistan is doing little to stem the flow of a resurgent Taliban who have launched a new offensive in Afghanistan from Pakistan.
At the weekend the head of the upper house of the Afghan parliament, Sibghatullah Mujaddedi, accused the Pakistani secret service of being behind a suicide bombing which injured him and killed four other people in Kabul.
Pakistan has strenuously denied the charges, accusing elements in the Afghan government of a disinformation campaign.
A resurgent Taliban and their Islamist allies have launched waves of attacks in which 1,500 lives, including 100 Americans, have been lost in the past year.
The director of the US Defence Intelligence Agency, Lieutenant General Michael Maples, recently told the Senate's Armed Forces Committee in Washington that the Taliban and their allies were at their most powerful since the official end of the war five years ago. He and other US and British commanders expect a major Taliban offensive starting in the spring.
Stingers began to be delivered to the Afghan mujahedin by the Reagan administration in 1986. They proved extremely successful against the Russians' main helicopter-gunship, the Hind-D, and were a significant contributory factor in the full Soviet withdrawal from Afghanistan three years later.
More than 2,000 Stinger missiles were sent by the US. An effort by the CIA to buy them back after the war was largely a failure. In 2001 Pentagon officials said some of the missiles might have fallen into the hands of the Taliban and al-Qa'ida.Reuse content