Depleted uranium shells fired by Britain in the Gulf war and the US in Kosovo contained traces of plutonium and other highly radioactive particles, the Ministry of Defence and the US department of energy admitted yesterday.

The fact that DU rounds used by British and US forces contain far more radioactive isotopes than uranium, which are more likely to cause cancer, is bound to fuel the controversy over Gulf war syndrome.

But the additional risk to British and US servicemen was minimal because the amounts of contaminants were so small, a MoD spokeswoman in London said yesterday, echoing a Nato statement issued in Brussels.

The International Atomic Energy Agency in Vienna was not so sure that the dangers of uranium containing even traces of plutonium were small, saying there was no data on what happened to contaminated depleted uranium when released into the atmosphere.

David Kyd, spokesman for the agency, said: "The science simply can't provide the answers in terms of the long-term consequences. It is definitely worth investigating further, not only in the Balkans but also in Iraq."

In Germany, the defence minister, Rudolf Scharping, yesterday summoned the US charge d'affaires in Berlin to brief him on the issue.

The Ministry of Defence said the increase in radiation dose to British servicemen handling the shells and operating in tanks with DU shielding because of the contaminates was only 0.8%, so small as to be minimal.

However, other experts disagreed. John Large, of Large Associates, said: "Once this has been fired in anger and is lying about in dust, there is a huge difference in the dangers. A speck of plutonium is hundreds of times more dangerous than uranium."

Mr Large said the only way that products of nuclear fission known as transuranics - neptunium, plutonium, and americium - could get into depleted uranium was through reprocessing. "I am amazed they have done this."

Both the US and UK defence organisations denied the uranium had been reprocessed. The uranium had been supplied from the same civil source in the US and had accidently been contaminated because it had been placed in the same containers as reprocessed material.

Mr Kyd emphasised that the research so far on the effects of DU was derived from monitoring miners dealing with natural uranium or the consequences of the Chernobyl nuclear disaster.

Over the past 10 years of controversy about the impact of particles released when DU shells hit their target, there had been no civilian research on the battlefield until Nato told the UN where to find sites it examined in Kosovo last year.

The IAEA, which is taking part in the UN investigation, was offered some information about the effects of DU munitions by military sources, but Mr Kyd said it was "still sketchy on what happens after vaporisation".

Mr Scharping also ordered a German laboratory, testing samples from Kosovo, to look specifically for traces of plutonium. The University of Bristol is also testing Kosovo samples of depleted uranium.

Mr Scharping made the move after it became known that a German television programme to be transmitted tonight by the publicly-owned ARD channel will turn the spotlight on documents from the US Department of Defence which noted the possibility of plutonium traces in its weapons.

A spokesman for the US embassy in Berlin said the documents were openly available on US government websites.

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