Another US soldier has been killed by hostile fire in Iraq - the fifth in the past 24 hours.
Attacks against US forces do not appear to be tailing off
Washington had hoped that after the deaths of Saddam Hussein's sons Uday and Qusay on Tuesday attacks on US forces would diminish.
But five Americans have been killed and seven wounded since early Saturday.
The latest incident involved a grenade attack on soldiers from the 1st Marine Expeditionary Force south of Baghdad, in which one man died.
The BBC's Matthew Price in Baghdad says Washington puts the violence down to forces loyal to the former regime, but others point out there is much resentment against the Americans.
The US will have to consider the possibility that even if it can wipe out the remnants of Saddam Hussein's regime, its troops will continue to come under attack as long as they remain on Iraqi soil, our correspondent adds.
Saddam 'guards' held
On Saturday, three soldiers were killed and four wounded when they came under grenade attack while guarding a children's hospital in Baqubah, northeast of Baghdad.
Later, another soldier was killed and two wounded when their convoy was attacked with small arms, rocket-propelled grenades and possibly also an improvised explosive device in the Abu Ghuraib district of the capital.
Those killed in the Baqubah attack were from the 4th Infantry Division, which was involved in an operation on Thursday against Iraqis suspected of being Saddam Hussein's bodyguards.
The latest deaths bring to 49 the number of US soldiers killed in Iraq since President George W Bush declared the war was over.
US Central Command says it is not drawing a link between the deaths and the recent high-profile operations, including the killing of Uday and Qusay Hussein.
On Saturday, US army engineers began to demolish the villa in Mosul where the brothers were killed, after it was scoured for clues on the whereabouts of the deposed dictator.
Thirteen people were arrested during a raid near Saddam Hussein's home town of Tikrit on Thursday, and up to 10 are thought to have served as his personal bodyguards.
The arrests, which apparently came after a tip-off, are being described by the Americans as a real boost in their hunt for the fugitive Iraqi leader.
US troops have voiced dismay at their mission extension
In a separate incident on Saturday, Baghdad's newly appointed police chief, Brigadier Ahmed Kadhim was injured in a clash with suspected hijackers and kidnappers in the Iraqi capital.
Brigadier Kadhim was shot in the leg, and five of his officers were wounded, one critically, as they pursued a group of suspects in the north of the city.
The police chief is now recovering in hospital and all the suspects have been apprehended, but the BBC's Mike Donkin in Baghdad says the incident highlights growing concern among Iraqis about violent crime since Saddam Hussein was ousted.
Kidnappings and car hijackings have been on the increase in Baghdad since the war ended and a number of street gangs have been formed.
Saddam wife 'quizzed'
US officials have said they hope the deaths of Uday and Qusay Hussein will weaken anti-American resistance and lead coalition forces to Saddam himself.
"We continue to tighten the noose," said Major General Ray Odierno, commander of the US Army's 4th Infantry Division.
He said there had been an increase in the flow of information coming to them since the deaths of the brothers - two of the most feared members of the old regime.
The US military had also questioned one of Saddam's two wives, Associated Press quoted the general as saying.