That makes it difficult for Iraqi soldiers to move in or out of Baghdad.
US defence officials also say that the first tests on a number of chemicals found near the city of Karbala show they may have substances that could be used in chemical and biological weapons.
There have been worries that Saddam Hussein would use such weapons against the British and American troops.
But the Americans are also saying that they need to do more tests before they can be sure they are right.
The Iraqis say the US troops aren't even in Baghdad and that they have managed to kill many American soldiers.
They've also shown television pictures of Saddam with his son and other senior figures in his government.
Other main points
- It's thought the top commander in the south of Iraq, known as Chemical Ali is dead
- 2 American soldiers and two journalists dead and many others injured in an Iraqi rocket attack on US command centre near Baghdad
- At least two US marines are killed and many are injured as they fight to capture bridges in the south-east of Baghdad
- UK troops push into Basra and set up control over Iraq's second city
- The northern city of Mosul is bombed heavily