Chemicals expert held for questioning about weapons of mass destruction

US forces questioned their biggest catch in the war so far yesterday: a top Iraqi scientist who surrendered after learning he was on America's "most wanted" list.

Lieutenant-General Amer Hammoudi al-Saadi, a British-educated chemicals expert who previously headed the Iraqi delegation at UN talks on disarmament, is described as a "big fish" by the UN monitors. He holds the key to the truth about Saddam Hussein's weapons of mass destruction.

However, before he was driven to an undisclosed location after handing himself in to the US army on Saturday, he continued to deny that Iraq still holds any chemical or biological weapons.

The Defence Secretary, Geoff Hoon, said yesterday: "We are hoping to get some useful information out of him, and indeed out of others, as increasingly we take more territory and identify those individuals who should have useful information about the weapons programmes."

US Marines yesterday discovered 278 artillery shells which they said tested positive as a blistering agent. The shells were found in trailers parked in a schoolyard. But they said more tests would be needed before any conclusions can be drawn.

Although Allied governments and their military commanders remain confident that they will eventually detect weapons of mass destruction, the head of US Central Command, General Tommy Franks, acknowledged that none had yet been found despite the discovery of a series of suspicious items. "I have not found any that I have absolutely satisfied myself are ... weapon of mass destruction materials," he said.

Differences have begun to emerge between the US and British governments over the verification of weapons of mass destruction finds.

Tony Blair said last week that any banned weapons finds would have to be "externally verified", perhaps by the UN. His point was taken up by the UN secretary general, Kofi Annan, who stressed that the UN monitors were the sole legitimate international authority, "and when the situation permits they should go back to resume their work".

But the US Secretary of State, Colin Powell, repeated yesterday the US view that it was not necessary to involve the United Nations in the search for banned weapons.

A US team has already been set up to question Iraqis involved in weapons programmes, while others search sites and analyse samples in the field. There are fears, however, that an American team would not be sufficientlyneutral to be considered objective.

Mr Hoon, said in a BBC interview: "I think it is important that we have an objective source of verification." But he was critical of the UN inspectors' record in Iraq, and noted that the Allies had not decided whether such verification should come from UN weapons inspectors or "some other international body or some other country that has a tried and tested reputation for objectivity in this area."