Jill Carroll, a 28-year-old freelance reporter for The Christian Science Monitor, has not been heard from since she was grabbed Jan. 7 in one of the city's most dangerous neighborhoods. Gunmen ambushed her car and killed her translator shortly after she left the offices of a Sunni Arab politician.
The U.S. Embassy said it was working with local authorities "and doing everything possible to bring about her safe release."
An Iraqi Interior Ministry official said police were taking the matter "very seriously."
"We are doing our utmost to find her or reach her. The search continues," said Gen. Hussein Kamal, deputy interior minister in charge of domestic intelligence.
In other developments:
The Boston-based Christian Science Monitor said Saturday that it continued "to pursue every possible avenue" to win Carroll's release.
"This has been a difficult week for Jill's family and for us," Richard Bergenheim, the Monitor's editor, said in a statement.
"Jill's deep love for Iraq and the Iraqi people have come out in the published statements by a number of her Iraqi friends and fellow reporters. She is committed to helping the world understand the great good to be found in Iraq and its people, despite the struggles it is going through now."
The U.S. military raided a prominent Sunni mosque a day after Carroll was kidnapped, sparking a demonstration by hundreds of worshippers. A U.S. military official said the raid was a necessary immediate response to the kidnapping based on a tip provided by an Iraqi citizen. The military said last Sunday that six people were detained.
Carroll, who speaks some Arabic and wore a head covering while moving around Iraq, has been described by her editor as an aggressive reporter but not a reckless one.
Despite her language skills, Carroll used an Iraqi translator. The translator was slain by the kidnappers. The driver of their car escaped the attack and is now safe with his family, David Clark Scott, the Monitor's international news editor, said.
Police Maj. Falah Mohamadawi said the translator told officers just before he died that the abduction took place when he and Carroll were heading to meet a Sunni Arab political leader in the Adel neighborhood. The predominantly Sunni district is considered one of the toughest in Baghdad.
Meanwhile, Britain's Foreign Office revealed that a British journalist had been kidnapped in Iraq nearly three weeks ago but was freed by chance when U.S. soldiers raided the farmhouse where he was being held.
Phil Sands, a reporter for Dubai-based newspaper Emirates Today, was rescued Dec. 31 after being held captive for five days on the outskirts of Baghdad, the ministry said.
In an article published Saturday in Emirates Today, Sands recounted details of his abduction and said he felt "lucky to be alive." Sands said he was ambushed and captured after setting out with a local driver and interpreter to interview Baghdad academics.
"I was treated very respectfully and courteously apart from the fact that I was detained against my will and threatened with beheading," Sands told The Associated Press on Saturday. "I was not beaten, starved or treated badly."