Fragments of depleted uranium ammunition found in Kosovo were made with reprocessed fuel from nuclear reactors, the United Nations confirmed yesterday, raising new fears about the risks of contamination. Officials of the UN environment programme said tests on material gathered by its team of experts in Kosovo had revealed traces of uranium 236 - an isotope found only in spent nuclear fuel - among weapons delivered by Nato aircraft in the 1999 conflict.

The discovery came as the latest senior figure to enter the debate, the commander of British forces in the Gulf war, Sir Peter de la Billiere, called last night for a full public inquiry into claims that exposure to depleted uranium weapons had caused serious illnesses among British troops. He also suggested compensation for afflicted service personnel.

The latest DU discovery, which follows the investigation of eight of the 112 sites in Kosovo by a team of UN scientists last November, is likely to prompt questions about what other dangerous radioactive materials may have been contained in the US shells.

Futher analysis is being carried out in five European laboratories to determine radioactivity levels. The World Health Organisation and other international bodies have also been asked to give their as sessment of the implications of the finding.

There are two types of depleted uranium, known as "clean and dirty". Until now it has been assumed that the material used in US shells was of the clean variety which is obtained as a side-product of the extraction of uranium 235 from ore to make nuclear fuel or nuclear weapons.

By contrast "dirty" DU is what is left over when the fuel has been through a nuclear reaction. It is known as "dirty" because it may be contaminated with traces of far more dangerous isotopes such as plutonium and other highly radioactive particles.

"This is the first time that the spent fuel origins of DU munitions have emerged," David Kyd, a spokesman for the International Atomic Energy Agency, which is taking part in the UN's investigation, said last night.

The UN environment programme said in a statement last night that the amount of uranium 236 had been so small that it had minimal extra radioactive toxicity.

However, it said a final assessment would only be made once testing on spent ammunition, soil, water and milk samples collected in Kosovo is completed next month.  When British Nuclear Fuels supplied shells to the MoD for use in the Gulf war, it used clean DU. But in 1993, according to documents seen by the Guardian, 120,000kg of DU were imported from the US for use in munitions.

None of this was used by British forces in Kosovo although tanks with this ammunition on board were ready for deployment. Last night it was not known whether the DU imported into Britain was clean or dirty.

The likely explanation of how dirty DU came to be used in Kosovo is one of cost and ease of access by the US military. In the privatised world of US nuclear utilities the clean DU would belong to private companies.

In the possession of the government would be stockpiles of dirty DU left over from the cold war when the US military reprocessed thousands of tonnes of spent nuclear fuel to extract the plutonium. For every tonne of plutonium gained, 100 tonnes of dirty DU would have to be stored.

In the 1980s and 1990s all four big nuclear powers - Russia, US, UK and France - began converting stockpiles of otherwise useless DU into armour piercing weapons. It was not until last night that anyone outside military circles realised that some of it was dirty DU.

Meanwhile, it emerged that General Sir Peter de la Billiere confirmed he was not warned that DU weapons could pose a radiation danger.

Sir Peter's intervention will be welcomed by Gulf war vet erans convinced the shells have led to serious illnesses.

Asked by the BBC News if he supported calls for a full public inquiry into DU weapons, Sir Peter replied: "Of course, for two reasons. If indeed there is a proven link to illnesses (veterans have) got to be looked after and receive proper compensation."

Secondly, he said, it was critically important to establish whether there was a link because if there was not, the military would want to go on us ing the weapons.

Asked if he was warned about DU weapons - fired by British tanks as well as American armour and aircraft during the Gulf war - Sir Peter said: "I was not aware there were any specific dangers to it."  He added that British commanders wanted to make sure they had the "best equipment on the market".