The US has launched a new operation against insurgents in Iraq, backed by hi-tech missiles, fighter jets and attack helicopters.
The United States is responding to mounting attacks on its forces
US forces fired a satellite-guided missile at a "guerrilla camp" about 25km (15 miles) west of Kirkuk, for the first time since major combat ended.
Operation Ivy Cyclone Two is targeting insurgents in north-central Iraq.
It comes after at least 17 Coalition troops died when two Black Hawk helicopters were downed in Mosul.
Lieutenant-Colonel Bill Macdonald, spokesman for the 4th Infantry Division base in Tikrit, said the operation marked a "more aggressive" approach in the region.
"We want to demonstrate that we have the capability to co-ordinate operations simultaneously over a large area," he said.
US forces are changing tactics in response to the rising number of attacks on coalition forces - and casualties - since President Bush declared an end to major combat in Iraq on 1 May.
Iraqis have also been killed in substantial numbers, with one recent estimate putting the number of deaths at more than 200 since May.
Lieutenant-Colonel Macdonald said the guided missile - with a 500 pound warhead - was fired from a mobile launch pad just north of Baghdad on Sunday.
He said it hit a guerrilla training centre on an island on the Little Zab river west of the city of Kirkuk.
"It is the first time since the end of major combat that a munition of this type has been used," he told reporters.
Meanwhile, an Arabic TV station on Sunday broadcast an audio tape purported to be ousted Iraqi dictator Saddam Hussein, calling on Iraqis to wage holy war against occupying forces.
"Fighting them...is a legitimate, patriotic and humanitarian duty and the occupiers have no choice but to leave our country Iraq, the country of Arabs and Islam, as cursed losers," the speaker said.
Later on Sunday, correspondents reported hearing a series of explosions in the capital, although there was no immediate confirmation of their cause or location.
Iraq's civil administrator Paul Bremer - in a series of US TV interviews - said there was no doubt the US was "in a tough fight" in Iraq.
"We have some determined opponents. Particularly the international terrorists who have been coming into the country in the last four or five months," he told Fox television.
"But if you look at the polls here... they tell us that a large majority of the Iraqi people want American coalition forces to stay here until the place is stabilised," Mr Bremer said.
US HELICOPTER CRASHES IN IRAQ
15 Nov - Two Black Hawks crash in Mosul, at least 17 killed
7 Nov - Black Hawk shot down near Tikrit, six killed
2 Nov - Chinook shot down near Falluja, killing 16 US soldiers
25 Oct - Black Hawk crashes near Tikrit, reportedly hit by ground fire - soldier injured
Meanwhile, the US army in Iraq is examining the wreckage of the two Black Hawk helicopters which crashed in the northern city of Mosul.
Some witnesses said one of the helicopters was hit by ground fire and then collided with the second aircraft.
Seventeen soldiers were killed, five were injured and one is still missing after the crash, which hit 101st Airborne Division forces.
Five US helicopters have crashed in the past three-and-a-half weeks in Iraq with the loss of 39 lives.
The US-led coalition said one helicopter was carrying a quick reaction force and the other was carrying soldiers on a transport mission.
According to an unconfirmed report, the tail of one helicopter was hit by a rocket-propelled grenade.
On Saturday, the US-appointed Governing Council unveiled an accelerated timetable to transfer the country to Iraqi control, saying the Coalition would hand over power to a transitional government by June 2004.
Bremer (centre) plans to end US occupation next year
The transitional body will prepare for a full sovereign Iraqi government by 2005, following a general election.
Council President Jalal Talabani - speaking after the meeting with chief US administrator Paul Bremer - said the transitional body would be selected after consultations with "all parties" in Iraqi society.
US Defence Secretary Donald Rumsfeld insisted that the new schedule would not affect the US military presence.
"This has nothing to do with coalition troops in Iraq," he told reporters in Japan where he is on a visit.
Paul Bremer also told US television that a new Iraqi government - once it assumes power - would keep US troops in the country.
"I'm sure the Iraqi Government is going to want to continue to have coalition forces here for its own security for some time to come," he said on ABC's This Week programme.
On CNN's Late Edition he denied it was a major shift in US policy to drop the demand Iraqis draft a permanent constitution before getting power back.