Iraqi paramilitaries loyal to President Saddam Hussein had been passing themselves off as civilians in the southern city of Basra and were liable to attack by allied forces, according to a US military spokesman.
"We have seen a number of people dressed as civilians with weapons entering and leaving Basra," Brig Gen Vincent Brooks claimed at a news conference at US Central Command (known as "Centcom") headquarters in Qatar yesterday.
Describing the paramilitaries as "terrorists", he said they were a potential target of allied fire. "As we determine a hostile act, yes, we do fire in those cases against those types of target that are presented," he said.
"That's what the modus operandi is of these terrorist squads, these paramilitaries that are out there. As we have encounters, we engage in combat with them and generally we defeat them."
He claimed Iraq may have prepared its forces to use chemical weapons if allied forces advanced beyond a certain line, although he had seen no signs the final order to use them had been given.
"I have not seen anything that says that an order has been given to fire. We know that the capability does indeed exist, we know that the will exists and we are taking this very, very seriously."
The US military has already said it fears the Iraqi regime might use chemical weapons if allied forces get close to Baghdad.
"There might be trigger lines that are out there or places at which the regime would feel threatened enough that they would use (chemical weapons) and, as we add the additional evidence we have found on the battlefield, we begin to take that very seriously," Brig Gen Brooks said.
"We've seen chemical protective equipment in a number of areas south of where we thought that red line might be."
He said a total of 12 medium-range missiles had been launched into Kuwait from Iraq, but all those considered "threatening" had been intercepted by US Patriot anti-missile devices.
"I don't think we know exactly how many launchers the Iraqis have of any particular family of weapons systems. Only the Iraqis really know," he said. "Is there an intent to continue a threat to neighbouring countries? Absolutely."
He added: "Because of the development of expanded-range weapons systems by the Iraqis ... we believe that Iraq still poses a threat to many of its neighbours by way of missiles."
He was asked for his reaction to a statement by Lieut Gen William Wallace, the US army's senior ground commander, that "the enemy we're fighting is different from the one we'd war-gamed against".
Brig Gen Brooks said: "Our enemy always has a vote in how the circumstances go. I don't think that we have necessarily underestimated (the enemy). No one can ever predict how battle will unfold."
However, he acknowledged that there was a different view of the situation at the headquarters level from that among commanders on the ground. "There is a different view down on 'Planet Earth', the closer you get to the line," he said.
"We know that we have to be tactically patient," he added. "I don't think we have necessarily underestimated and I am certain that we account for the enemy. I think we remain confident that we have a good grip on what is going on here."
While the flow of supplies to the thousands of US troops advancing towards Baghdad had been temporarily slowed down because of bad weather, "we're still able to conduct operations as we see them and we're still on our plan".
The Iraqi Information Minister, Mr Mohammed Said al-Sahhaf, had earlier dismissed US suggestions that the discovery of protective clothing against chemical weapons meant Iraq possessed such devices, claiming the suits were normal precautions for any army.