"It's great to have them off," Lieutenant Colonel Fred Padilla, commander of the 1st marines battalion, said after his troops stripped down to lighter camouflage garb.

US military officials said an order allowing removal of the suits, which troops said felt like heavy raincoats and thick rubber boots under a hot sun, had come down for the 20,000-strong 1st Marine Division.

"They made an assessment and they determined there was not a serious threat right now," Padilla said.

Brigadier General John Kelly, assistant commander of the 1st Marine Division, said field commanders would take the final decision whether their troops could take off the cumbersome garb.

But the order was welcome news to the marines pushing towards Baghdad from the southeast in a bid to complete the encirclement of the capital.

The possibility a cornered Saddam Hussein might unleash his suspected arsenal of chemical or biological weapons has haunted the US-led forces since they launched their invasion of Iraq on March 20.

But after crossing a much-vaunted but unspecified "red line" around Baghdad that was said to be the trigger for the use of such arms, US forces have become increasingly confident the threat was much reduced if not eliminated.

Commentators said the Americans had driven too close to the Iraqi defenders, who would be hesitant to throw any chemical weapons at them for fear they may blow back in their own faces.

Kelly said the speed of the US movements also provided a margin of safety.

"In order for him (Saddam) to unleash chemical weapons, he needs to know where you are," the general told AFP. "If you are moving, it makes it more difficult."

The fact also remained that with US and British forces in control of a substantial part of Iraq 19 days into their offensive, they have yet to find any hard evidence of chemical or biological arsenals.

They have found Iraqi gas masks and chemical protection suits; they also discovered what they believed was a training school for nuclear, chemical or biological warfare. But they have yet to turn up a "smoking gun."

US military officials told AFP last week the threat of an Iraqi chemical or biological attack had been greatly diminished. The 101st Airborne Division gave its troops the green light four days ago to doff their protection suits.

"Now that we have penetrated Baghdad's outer ring, the likelihood (of such an attack) is negligible," said Captain Adam Mastrianni, the intelligence officer of the division's Aviation Brigade.

US war planners had feared Saddam might launch a chemical attack when invading troops reached three zones: the holy Shiite city of Karbala 100 kilometers (60 miles) southwest of Baghdad, the capital's outskirts and the city interior.

But US forces have moved into all three without any chemical riposte. Mastrianni also saw politics as a factor.

"We think that, quite frankly, even if Saddam Hussein is in control, which is still debatable, he's paralysed by the fact he knows he will be prosecuted over war crimes," Mastrianni said.

"If he somehow survives this, and if he doesn't use them, then he looks kind of like the victim to the Arab world," he added.

SPACE.WIRE