LONDON - Depleted uranium munitions are suspected of leaving a lasting legacy of illness and death. NATO will investigate suspicions that contact with them has killed some of its own peacekeeping troops in the Balkans.

Following are background facts about depleted uranium weapons:

WHAT DEPLETED URANIUM IS

• It is a man-made by-product of the processing of mined uranium ore. The most radioactive isotopes of uranium are extracted for use in nuclear weapons and civilian reactors. Left behind is the less radioactive isotope 238: depleted uranium.

WHY IT IS USED

• Weapons scientists began in the 1970s to incorporate depleted uranium into the casings and tips of conventional, non-nuclear missiles, shells and bullets. Its great density adds penetrative power to munitions used against tanks or other armoured vehicles, and it can burn on impact. Use of depleted uranium in armour plating increases its strength.

WHO HAS THE WEAPONS

• The US military, several other NATO countries and Russia are known to possess depleted uranium weapons, while Israel, some Arab states and some Asian armies are assumed to have them.

WHERE THEY HAVE BEEN USED

• Never used in warfare before the 1990s, depleted uranium munitions are known to have been fired in anger only by Western forces. By far their greatest use was during the 1991 Gulf War - declassified US documents show that US forces fired about 944,000 cigar-sized rounds in Iraq and Kuwait.

  The Pentagon, under pressure from critics who accused it of covering up the issue, said last year NATO forces fired much fewer - 31,000 rounds - against Yugoslav armoured vehicles in the 1999 Kosovo conflict. Some 10,000 were fired in neighbouring Bosnia in 1994-95, NATO officials reported only last month.

  US forces have also been accused of firing depleted uranium munitions during training exercises in other parts of the world.

THE ALLEGATIONS

• The scale of the threat posed by depleted uranium is hotly disputed. But experts agree the toxic and radiological hazard is heightened by the tendency of depleted uranium to be pulverised on impact into a fine radioactive and toxic dust which stays in the environment, or the body, for many years.

• Iraqi authorities blame thousands of civilian cancer deaths and deformities in babies on contamination by Western depleted uranium weapons. Critics counter that the casualties might in fact be victims of Iraq's own chemical arms.

  "One single particle of depleted uranium lodged in the lymph node can devastate the entire immune system," Dr Roger Coghill, a Wales-based experimental biologist, told a London conference dealing with links between depleted uranium and cancers in Iraq.

• US veterans' groups say depleted uranium weapons are partly to blame for a vast range of health problems among thousands of veterans who fought in the Gulf War. A Pentagon report last month called such a link "unlikely".

• A UN report in May 2000 warned that much of Kosovo's water could be so contaminated as to be unfit to drink, and that a clean-up of the province could cost billions of dollars. It warned UN staff in the province not to approach any target which might have been hit by a depleted uranium weapon.

  Both Serbian and Kosovo Albanian media and authorities have voiced fears over the long-term pollution of soil, air and water by particles of depleted uranium. Belgrade says that several areas of Serbia proper, as well as Kosovo, were attacked with depleted uranium weapons.

• Italy has demanded that NATO investigate alleged links between the deaths of six of its soldiers from leukaemia after tours of duty in Kosovo and Bosnia - the so-called "Balkans syndrome" - and depleted uranium weapons.

• Belgium, five of whose soldiers are alleged to have died of suspicious illnesses after Balkan duty, and Portugal, with one alleged victim, joined the Italian appeal.