A full-scale US-led assault on the insurgent-held Iraqi city of Falluja is taking place - an attack which has been threatened for weeks.
US-led troops earlier seized control of the main hospital
Up to 15,000 US and Iraqi government troops are involved, backed by aircraft, tanks and artillery.
Witnesses report explosions and flares lighting up the sky, and the noise of battle echoing across the city.
The top US commander in Iraq, Gen George Casey, said there would be a "major confrontation" inside Falluja.
US Defence Secretary Donald Rumsfeld described the insurgents as assassins, terrorists and the remnants of deposed Iraqi leader Saddam Hussein's regime.
The BBC's Paul Wood, who is travelling with one American unit - and whose reporting is subject to military restrictions - reports that US-led forces are gradually forcing their way into the city.
He says it has been an evening of heavy air strikes and tank advances, punctuated by several huge explosions - some of them caused by devices used to detonate roadside bombs, others by weapons caches being detonated.
The main hospital and railway station have already been taken.
Although many of Falluja's residents had left the city ahead of the assault, it is thought that 100,000 civilians could remain in the city.
A US military spokesman estimated that 42 insurgents
were killed across Falluja in the bombardment and skirmishes
before the main assault began.
Two US marines died when their bulldozer turned over into the Euphrates River near Falluja earlier on Monday.
A doctor at a clinic in Falluja, Mohammed Amer, reported
that 12 people in the city had been killed. Seventeen others - including a five-year-old girl and a 10-year-old boy - were wounded, he added.
The head of the committee of Falluja residents which had been negotiating with the Iraqi government before the assault said the city was completely surrounded.
Speaking from outside the city, Khaled al-Jumaily also told the BBC Arabic Service that American and Iraqi government forces had damaged equipment at the hospital, arrested staff, and cut off roads, medical supplies, water and electricity.
He again blamed the authorities for the failure of the talks.
In other developments:
An explosion outside one of the main hospitals in the Iraqi capital Baghdad kills at least three people
Car bombs explode outside two Baghdad churches, killing three people and injuring more than 40 others
A British soldier is killed and two more are injured in a reported roadside bomb attack near their base south of Baghdad
An American soldier dies after his patrol is fired
on in eastern Baghdad
Iraq will hold elections in January,
despite European Foreign Minister Javier Solana's statement casting doubt on
the deadline, the White House says
Gen Casey confirmed that between 10,000 and 15,000 US and Iraqi troops were involved in the operation, and were facing an estimated 3,000 insurgents inside the city.
He said the mission had been codenamed "Al-faja" ("dawn"), a name chosen by the interim Iraqi Prime Minister, Iyad Allawi.
Prime Minister has power* to:
Restrict freedom of movement, assembly and use of weapons
Cordon off and search suspect areas
Freeze assets of suspected insurgents
Conduct military and security operations in suspect areas with the aid of US-led multinational forces
*Under the National Safety Law passed in July
"What we have generally seen is that there is an
outer-crust of the defence, and... they will probably fall back and go toward the centre of the
city where there be probably a major confrontation," he said.
Gen Casey also said he believed some 50-70% of the civilian population of 200,000 had left the city.
At a Pentagon news conference, Mr Rumsfeld said insurgents based in the city were
determined to resist.
"I think it's a tough business, and it's going to take time," he
Mr Allawi gave the go-ahead for the assault, which is designed to re-establish government
control before January's planned elections.
He also announced
a round-the-clock curfew in Falluja and another nearby
insurgent stronghold, Ramadi, under emergency powers he
was granted the day before.
"The people of Falluja have been taken hostage... and
you need to free them," he told Iraqi
soldiers during a visit to the main
US base outside Falluja just before the attack began.
Asked to comment on the start of the Falluja assault,
United Nations spokesman Fred Eckhard reiterated that
Secretary-General Kofi Annan believed force was sometimes
necessary, but was concerned that the attack could "destabilise
the country at a critical point in the preparation for the
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.
Jordanian-born militant Abu Musab al-Zarqawi, said to be behind the kidnapping and killing of foreigners in Iraq, has urged resistance against the US-led attack and said victory will come "in a matter of days".