US-led troops seized control of a hospital in the west of the cityUS-led forces have begun a full-scale attack on the insurgent stronghold of Falluja in central Iraq.
The move, which had been expected for weeks, came after interim Iraqi Prime Minister Iyad Allawi gave the go-ahead.
The BBC's Paul Wood reports very heavy fighting and the sound of massive explosions as US and Iraqi government troops battle their way into the city.
Earlier, they took control of the city's main hospital and two bridges over the Euphrates River.
Falluja is a predominantly Sunni Muslim city that has been a hotbed of resistance to the US-led occupation of Iraq following the toppling of Saddam Hussein's regime last year.
Many of its citizens have fled to escape the fighting, but there are still thought to be tens of thousands of civilians in the city.
Thousands of US and Iraqi troops, backed by tanks and aircraft, are attacking two northern areas of Falluja where insurgents are said to be massed.
Ahead of the assault, a massive aerial and artillery bombardment took place.
Our correspondent reports that the initial phase of the operation has seen the clearing of booby-trap bombs on the main routes into the city.
He says a US marine officer has told him that huge 2,000lb bombs have been dropped on insurgent positions from aircraft.
Darius's note: Any civilians down there?