Iraqi aircraft today shot down a US unmanned surveillance drone over southern Iraq , US military officials said.

The Predator drone was conducting a reconnaissance mission and the plane is presumed destroyed, a senior US official said. Iraqi fighter aircraft penetrated the no-fly zone in southern Iraq and fired on the Predator, and its controllers then lost contact with the plane, US officials said.

"This action is the latest chapter in a lengthy list of hostile acts by the Iraqi regime," said Jim Wilkinson, a spokesman for central command, which oversees operations in Iraq and the surrounding countries.

Iraq's action can be seen as an act of defiance at a time when the US and Britain appear to be accelerating military plans for a showdown with the Iraqi leader, Saddam Hussein.

Earlier today the US dismissed as "a stunt" an Iraqi offer to admit CIA agents to help arms inspections, as scores of UN arms experts swooped on at least three sites near Baghdad.

Iraqi officials said a biological weapons team from the UN monitoring, verification and inspection commission (Unmovic) spent two hours at what the officials described as a closed baby milk plant in Abu Ghreib, 16 miles west of Baghdad.

Youssef Taher, head of the facility, said the plant closed three years ago due to the high cost of producing milk locally compared to importing it. He told reporters after the visit the inspectors asked about the production process, raw materials and chemicals that had been used before it was shut down.

"It was an ordinary visit and we answered all their questions," Mr Taher said, adding that the plant had been visited by previous inspection teams. He did not say what banned material the plant had been suspected of producing.

In other visits, a UN chemical team inspected the Ibn Bitar animal vaccination facility some six miles north of the capital and another team went to the headquarters of Faw Engineering Company, run by Iraq's military industrialisation commission.

As the US rebuffed Iraq's latest offer, Baghdad unleashed a fresh wave of invective against the Bush administration. An Iraqi government newspaper said the US president, George Bush, was using lies to justify a war against Iraq.

"The administration of little Bush is launching a mad campaign based on lies and accusations in order to divert public attention from reality and find excuses for an aggression against Iraq," the ruling Baath party newspaper al-Thawra said in a front page editorial.

The war of words was intensifying as it emerged that Israel and the US are to stage a joint exercise this week to integrate two different anti-missile systems.

Israel is concerned that Iraq might attack in retaliation for a possible US offensive against Iraq. Zalman Shoval, an adviser to the Israeli prime minister, Ariel Sharon, said: "Israel will also increase its activities in the coming weeks because the Americans and the other parties, based on their announcements, are speeding up their preparations for a possible attack on Iraq."

Hundreds of US soldiers are to arrive in Israel this week with US-made Patriot anti-missile batteries.

In the UK, the Ministry of Defence played down reports of imminent military action as reports emerged at the weekend of a possible amphibious assault to seize the southern Iraqi port of Basra that would involve Royal Marines.

The MoD dismissed the Sunday Telegraph report of such an assault as "speculation". A Downing Street spokesman added: "No decision has been taken on military action. We want a peaceful solution. The choice is Saddam's."

But statements from Washington were more bellicose in what could be construed as a good cop, bad cop routine between Britain and the US. A US official said the campaign to rid Iraq of any weapons of mass destruction was nearing an end.

"While we have not given up on disarming Iraq through the United Nations, we are now entering a final phase in how we compel Saddam Hussein to disarm," the official told Reuters.

Meanwhile, more religious figures weighed in against war as the Bishop of Bath and Wells today became the latest churchman to speak out against war in Iraq, warning that it would unleash "evil" across the Middle East.

"I don't doubt for a moment that evil should be confronted, but there is a way of confronting evil that doesn't involve even more evil," said Bishop Price. "And the real question that we have to face in going into a conflict situation in the Middle East is just what evil will be unleashed?"