By Paul Danahar
BBC Asia bureau chief, Beijing
Britain has privately complained to Beijing that Chinese-made weapons are being used by the Taleban to attack British troops in Afghanistan.
A large number of British troops are based in Afghanistan
The BBC has been told that on several occasions Chinese arms have been recovered after attacks on British and American troops by Afghan insurgents.
The authorities in Beijing have promised to carry out an investigation.
This appears to be the first time Britain has asked China how its arms are ending up with the Taleban.
At a meeting held recently at the Chinese foreign ministry in Beijing, a British official expressed the UK's growing concern about the incidents.
When asked about the latest British concerns, the Chinese foreign ministry referred back to a statement made by their spokesman Qin Gang in July who said China's arms exports were carried out "in strict accordance with our law and our international obligations".
For their part, the Taleban have recently begun boasting that they have now got hold of much more sophisticated weaponry although they refused to say from where.
Afghan officials have also privately confirmed to the BBC that sophisticated Chinese weapons are now in the hands of the Taleban.
Taleban forces fled Kabul in 2001
They said these included Chinese-made surface-to-air missiles, anti-aircraft guns, landmines, rocket-propelled grenades and components for roadside bombs.
A senior Afghan official told the BBC: "Chinese HN-5 anti-aircraft missiles are with the Taleban, we know this... and we are worried where do the Taleban get them, some of these weapons have been made recently in Chinese factories."
Another Afghan official who deals with counter-terrorism said: "Serial numbers and other information from most of the Chinese weapons have been removed in most cases and it's almost impossible for us to find out where they come from but we have shared our concerns with the Chinese and the Americans also."
The Afghan government considers China to be a friend, and a much less meddlesome ally than the other big player in its neighbourhood, India.
But, the counter-terrorism official added, "China is worried about the presence of the US in the region".
Southern Afghanistan has been awash with Chinese made arms for decades which are some of the cheapest on the market.
In the past the Taleban got them via the Pakistan intelligence agency, the ISI, or bought them directly from arms smugglers.
But it is extremely unlikely the ISI would now allow them access to anti-aircraft missiles or armour-piercing ammunition.
Taleban regularly target foreign troops in Afghanistan
The Pakistani army's relationship between militants in its tribal areas along the Afghan border has deteriorated sharply in recent years after Washington put pressure on President Musharraf post-9/11 to crack down on al-Qaeda and Taleban groups operating inside Pakistani territory.
So the Taleban might well use any sophisticated new weapons it received against the Pakistani army.
It is not in China's interest either to arm Pakistan-based militants.
Over the last couple of years Chinese workers in Pakistan have been targeted by militants, in retaliation for the Pakistani army allegedly going after hard-line Muslim Uighur leaders from China's Xinjiang province, hiding in the tribal areas.
So instead of Pakistan being the transit point for these weapons, the finger is being pointed by many commentators towards Iran.
The Afghan government has long acknowledged privately that Iranian intelligence agencies have been active in southern Afghanistan post-9/11.
Iran has been pursuing a policy of building up proxy networks to be able to attack American forces in response to any US attacks against Teheran's nuclear infrastructure.
The Americans are suspicious of Iran's role in Afghanistan
A Shia Iran and the Sunni Taleban had been firm enemies since 1998.
Then, Iran threatened to invade western Afghanistan, when the country was largely controlled by the Taleban, after nine of its diplomats were massacred in Mazar-e-Sharif.
But times have changed, now America is a common enemy and senior American commanders in Afghanistan have acknowledged the growing ties between the two.
The complication for both the UK and US is China.
Unnamed US officials have recently been quoted as saying that China has been selling arms to Iran which Iran is then passing on to insurgent groups in Afghanistan and Iraq.
China's booming economy and its seat at the UN security council have made it an important player on the world stage.
It is a major trading partner for the UK whose economy has benefited enormously from China's cheap goods.
Prime Minister Gordon Brown's newly-appointed British Minister for Asia, Lord Mark Malloch Brown acknowledged to journalists in Beijing last week that countries "need to work with China to get things done in today's world".
China is going to have to show that getting things done also means stopping its arms illegally ending up in the hands of men bent on killing British troops.