A Swiss laboratory analysing munitions from Kosovo containing depleted uranium has also found traces of more radioactive enriched uranium, according to the United Nations Environment Programme (UNEP).
The UNEP said the laboratory in Spiez, canton Bern, had found traces of uranium 236 in weapons used by Nato during its campaign. But it said the quantities found were so small that the munitions were no more dangerous than those containing only depleted uranium.
"I can confirm that the Swiss found isotope U-236," UNEP spokesman Michael Williams said.
The UNEP sent a mission to Kosovo earlier this month amid growing fears that European troops who served in the Balkans could have been exposed to radiation, resulting in cases of leukaemia and other cancers. The agency collected samples of soil, water and vegetation, which are now being analysed in different laboratories.
On Tuesday, the Swiss defence ministry admitted it had tested weapons containing depleted uranium in the 1980s. It said it suspended the tests after finding the weapons were not much more effective than conventional ones.
A spokesman said the army had fired 16 shells containing uranium, before abandoning the experiment.
The admission followed an earlier report that the armaments company, Contraves, independently carried out tests with depleted uranium weapons about 30 years ago.
The revelations have heightened fears about the extent to which Swiss troops might have been exposed to radiation from the weapons.
The authorities have offered medical tests to all 900 soldiers who served in the Balkans since 1996.
swissinfo with agencies