Weapons of mass destruction will be found, insist Allies

US commanders said yesterday that they would need "detailed intelligence" to find the arsenal of weapons of mass destruction which they continue to insist has been hidden in Iraq.

The comments came shortly before US Marine combat engineers were reported by Fox TV – in the latest of a series of unconfirmed finds – to have found what could be weapons-grade plutonium at a site south of Baghdad called Al-Tuwaitha, a previously known weapons site visited several times by UN inspectors.

Twenty-two days after the invasion of Iraq, British and American forces have yet to confirm a finding of weapons of mass destruction. Iraq has strongly denied that it holds any chemical, biological or long-range ballistic missiles, in violation of UN resolutions. The Iraqis also say they have abandoned attempts to produce a nuclear weapon.

But Maj-Gen Victor Renuart, the US director of operations, said that "many of the places where weapons of mass destruction might be hidden are not obvious. We are going to have to use detailed intelligence and detective work to find them". US commanders have suggested that evidence might not come to light until the regime had fallen.

US Central Command in Qatar said that experts were still investigating two possible chemical finds on Monday – including 20 medium-range missiles which National Public Radio (NPR) in America reported could be equipped with sarin and mustard gas. Donald Rumsfeld, the US Defence Secretary, warned after those finds that caution was needed.

NPR quoted an official who said new US intelligence data showed the chemicals were "not just trace elements". It said the cache was discovered by marines with the 101st Airborne Division.

In the other case – on which some US officers have already cast doubt – possible toxic chemicals were discovered at a military compound and at an agricultural complex at Hindiyah, near Karbala. Victoria Clarke, a Pentagon spokeswoman, said last night that she had "no update" on these findings.

Fox were quoting Carl Prine, an embedded reporter from the Pittsburgh Tribune-Review about the possible plutonium find. He said nuclear and intelligence experts found 14 buildings with high levels of radiation. Tests found nuclear residue too deadly for human occupation, he added.

Mr Prine said radiation detectors went "off the charts" a few hundred metres outside the nuclear compound, according to Fox. Locals said "missile water" was stored in caverns there, he added.

Tony Blair has made it clear that he would like to see the UN weapons inspectors return to Iraq to help provide independent verification of any findings. It remains to be seen whether the US will agree. Last night, Ms Clarke referred a question about the issue to the State Department.

The red herrings

30 March British troops find protective suits, training materials and stocks of a nerve gas antidote, atropine, near Basra. Later confirmed to be for defensive purposes

31 March US military spokesman announces discovery of chemical protection suits and decontamination equipment near Nasiriyah. Later admits they could be for defensive purposes.

4 April US forces find hoard of white powder in boxes in military plant south of Baghdad. Substance turns out to be explosives.

6 April US forces find 14 barrels of chemicals that could be the nerve agents sarin and tabun. Further tests suggest the chemicals were pesticides.

7 April US military official says 20 medium-range missiles loaded with sarin and mustard gas found outside Baghdad. US Secretary Donald Rumsfeld treats report with caution saying: "Almost all first reports turn out to be wrong."

8 April Tony Blair says Iraq has weapons of mass destruction and that US and British forces will be led to them as Saddam Hussein's regime collapses.