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Did Israel use a secret new uranium-based weapon in southern Lebanon this summer in the 34-day assault that cost more than 1,300 Lebanese lives, most of them civilians?

We know that the Israelis used American "bunker-buster" bombs on Hizbollah's Beirut headquarters. We know that they drenched southern Lebanon with cluster bombs in the last 72 hours of the war, leaving tens of thousands of bomblets which are still killing Lebanese civilians every week. And we now know - after it first categorically denied using such munitions - that the Israeli army also used phosphorous bombs, weapons which are supposed to be restricted under the third protocol of the Geneva Conventions, which neither Israel nor the United States have signed.

But scientific evidence gathered from at least two bomb craters in Khiam and At-Tiri, the scene of fierce fighting between Hizbollah guerrillas and Israeli troops last July and August, suggests that uranium-based munitions may now also be included in Israel's weapons inventory - and were used against targets in Lebanon. According to Dr Chris Busby, the British Scientific Secretary of the European Committee on Radiation Risk, two soil samples thrown up by Israeli heavy or guided bombs showed "elevated radiation signatures". Both have been forwarded for further examination to the Harwell laboratory in Oxfordshire for mass spectrometry - used by the Ministry of Defence - which has confirmed the concentration of uranium isotopes in the samples.

Dr Busby's initial report states that there are two possible reasons for the contamination. "The first is that the weapon was some novel small experimental nuclear fission device or other experimental weapon (eg, a thermobaric weapon) based on the high temperature of a uranium oxidation flash ... The second is that the weapon was a bunker-busting conventional uranium penetrator weapon employing enriched uranium rather than depleted uranium." A photograph of the explosion of the first bomb shows large clouds of black smoke that might result from burning uranium.

Enriched uranium is produced from natural uranium ore and is used as fuel for nuclear reactors. A waste productof the enrichment process is depleted uranium, it is an extremely hard metal used in anti-tank missiles for penetrating armour. Depleted uranium is less radioactive than natural uranium, which is less radioactive than enriched uranium.

Israel has a poor reputation for telling the truth about its use of weapons in Lebanon. In 1982, it denied using phosphorous munitions on civilian areas - until journalists discovered dying and dead civilians whose wounds caught fire when exposed to air.

I saw two dead babies who, when taken from a mortuary drawer in West Beirut during the Israeli siege of the city, suddenly burst back into flames. Israel officially denied using phosphorous again in Lebanon during the summer - except for "marking" targets - even after civilians were photographed in Lebanese hospitals with burn wounds consistent with phosphorous munitions.

Then on Sunday, Israel suddenly admitted that it had not been telling the truth. Jacob Edery, the Israeli minister in charge of government-parliament relations, confirmed that phosphorous shells were used in direct attacks against Hizbollah, adding that "according to international law, the use of phosphorous munitions is authorised and the (Israeli) army keeps to the rules of international norms".

Asked by The Independent if the Israeli army had been using uranium-based munitions in Lebanon this summer, Mark Regev, the Israeli Foreign Ministry spokesman, said: "Israel does not use any weaponry which is not authorised by international law or international conventions." This, however, begs more questions than it answers. Much international law does not cover modern uranium weapons because they were not invented when humanitarian rules such as the Geneva Conventions were drawn up and because Western governments still refuse to believe that their use can cause long-term damage to the health of thousands of civilians living in the area of the explosions.

American and British forces used hundreds of tons of depleted uranium (DU) shells in Iraq in 1991 - their hardened penetrator warheads manufactured from the waste products of the nuclear industry - and five years later, a plague of cancers emerged across the south of Iraq.

Initial US military assessments warned of grave consequences for public health if such weapons were used against armoured vehicles. But the US administration and the British government later went out of their way to belittle these claims. Yet the cancers continued to spread amid reports that civilians in Bosnia - where DU was also used by Nato aircraft - were suffering new forms of cancer. DU shells were again used in the 2003 Anglo-American invasion of Iraq but it is too early to register any health effects.

"When a uranium penetrator hits a hard target, the particles of the explosion are very long-lived in the environment," Dr Busby said yesterday. "They spread over long distances. They can be inhaled into the lungs. The military really seem to believe that this stuff is not as dangerous as it is." Yet why would Israel use such a weapon when its targets - in the case of Khiam, for example - were only two miles from the Israeli border? The dust ignited by DU munitions can be blown across international borders, just as the chlorine gas used in attacks by both sides in the First World War often blew back on its perpetrators.

Chris Bellamy, the professor of military science and doctrine at Cranfield University, who has reviewed the Busby report, said: "At worst it's some sort of experimental weapon with an enriched uranium component the purpose of which we don't yet know. At best - if you can say that - it shows a remarkably cavalier attitude to the use of nuclear waste products."

The soil sample from Khiam - site of a notorious torture prison when Israel occupied southern Lebanon between 1978 and 2000, and a frontline Hizbollah stronghold in the summer war - was a piece of impacted red earth from an explosion; the isotope ratio was 108, indicative of the presence of enriched uranium. "The health effects on local civilian populations following the use of large uranium penetrators and the large amounts of respirable uranium oxide particles in the atmosphere," the Busby report says, "are likely to be significant ... we recommend that the area is examined for further traces of these weapons with a view to clean up."

This summer's Lebanon war began after Hizbollah guerrillas crossed the Lebanese frontier into Israel, captured two Israeli soldiers and killed three others, prompting Israel to unleash a massive bombardment of Lebanon's villages, cities, bridges and civilian infrastructure. Human rights groups have said that Israel committed war crimes when it attacked civilians, but that Hizbollah was also guilty of such crimes because it fired missiles into Israel which were also filled with ball-bearings, turning their rockets into primitive one-time-only cluster bombs.

Many Lebanese, however, long ago concluded that the latest Lebanon war was a weapons testing ground for the Americans and Iranians, who respectively supply Israel and Hizbollah with munitions. Just as Israel used hitherto-unproven US missiles in its attacks, so the Iranians were able to test-fire a rocket which hit an Israeli corvette off the Lebanese coast, killing four Israeli sailors and almost sinking the vessel after it suffered a 15-hour on-board fire.

What the weapons manufacturers make of the latest scientific findings of potential uranium weapons use in southern Lebanon is not yet known. Nor is their effect on civilians.