US forces in Iraq have struck at targets near Baghdad and elsewhere in a major offensive after a spate of deadly bombings and ambushes by insurgents.
US soldiers are anxious to glean accurate intelligence
President George W Bush stressed it was important for more Iraqis to provide intelligence to prevent new attacks.
US forces hit five targets near Baghdad airport with mortar fire on Friday - positions allegedly used by insurgents.
Earlier, a US helicopter gunship killed seven Iraqis suspected of preparing rocket attacks on a US base.
In the latest attack against coalition troops on Friday, a US soldier was killed and two others were injured in Baghdad.
The US military said the soldier from the 1st Armoured Division died in a roadside bombing in the centre of the city.
Two US soldiers were killed and three wounded in a roadside bomb blast on Thursday near Samarra, about 125 kilometres (75 miles) north of Baghdad, the US military said. They were travelling in a convoy at the time.
The US air strike near Tikrit was part of the operation aimed at rooting out insurgents in the Sunni Triangle - an area north and west of Baghdad where hostility towards US forces is widespread.
Tikrit was the home town of ousted Iraqi leader Saddam Hussein.
US troops later found hundreds of rockets and missiles at the scene, the US military said.
US jets also dropped satellite-guided bombs on a suspected insurgent target near the Syrian border, the military said.
President Bush said the latest US-led offensive was a response to the change in strategy by insurgents.
After a meeting with Italian President Carlo Azeglio Ciampi, he vowed once again to hunt down Saddam Hussein and transform Iraq into a democracy.
"We will stay until the job is done," he said. "And the job is for Iraq to be free and peaceful."
The BBC's Peter Biles in Baghdad says the tougher US action has the feel of a new phase in the occupation.
Despite the upsurge in Iraqi attacks, troops will stay on after the transfer of political power, the US has said.
Security has also been tightened in the southern city of Basra after the devastating suicide bomb attack on an Italian police base in Nasiriya on Wednesday.
More Iraqis have died in the guerrilla attacks than coalition troops - one estimate puts the toll at about 200 civilians since 1 May.
US raids around Tikrit have uncovered evidence that insurgents are operating in cells of up to 12 people, divided into groups of four with a strict chain of command, US Major Bryan Luke said on Friday.
"Whenever we go to detain someone in Tikrit, the relatives always say they're either in Falluja or Baghdad," Reuters quoted him as saying.
The American general commanding the military operation in Iraq, John Abizaid, said forces opposing US-led troops in the country totalled no more than 5,000 - the majority being Saddam Hussein loyalists.
US Central Command is beefing up its forward headquarters in Qatar, sending up to 300 extra staff from the main headquarters in Florida - a move aimed at responding more quickly to developments on the ground in Iraq.
In other developments:
At least four Iraqis were arrested early on Friday suspected of involvement in the downing of a US military helicopter a week ago.
In Basra, Coalition Provisional Authority (CPA) staff were confined to their headquarters following the threat of a possible attack. They were expected to remain there until Saturday evening.
A Portuguese journalist was kidnapped and another reporter injured by gunmen in southern Iraq on Friday.
A first group of 20 wounded Italians was airlifted to Rome, following Wednesday's attack in the southern town of Nasiriya that killed 18 Italians and nine Iraqis. The coffins of their dead comrades are due to return on Saturday.
An American civilian contractor was killed and another injured when gunmen attacked a convoy on Thursday near Balad, 70 km (45 miles) north of Baghdad.
US Defence Secretary Donald Rumsfeld has said Iraqis will get political power more quickly than had initially been thought.
"It does not mean that we would physically leave the country any sooner," Mr Rumsfeld said, adding it could take at least two years before troops withdrew from Iraq.