The Iraqi government said there were no women at the facilities.
Also on Saturday, a suicide bombing killed at least 19 and injured 67 people at a national guard recruiting station in the northern city of Kirkuk, an Iraqi Health Ministry official said. It was the third suicide bombing targeting Iraqi security forces in the past week.
On Saturday afternoon, two U.S. soldiers were killed and eight wounded by a vehicle bomb on the road to the Baghdad international airport. The soldiers were en route to the scene of a previous blast on the road that targeted a U.S. military convoy. Three soldiers were injured in that blast, which blew out windows in the area.
The video, played on the Internet and by Qatar-based Al-Jazeera TV network, showed the three captives kneeling blindfolded on the ground while a black-hooded gunman aimed his rifle at an American's head.
''My name is Jack Hensley. My job consists of installing and furnishing camps at Taji base,'' the American said nervously and swallowing hard. Fellow American Eugene ''Jack'' Armstrong and Briton Kenneth Bigley followed suit, giving their names and the same description of the job they have at the military base 15 miles north of Baghdad.
The gunman claimed to belong to the Tawhid and Jihad group led by Abu Musab al-Zarqawi, a Jordanian-born militant with links to al-Qaida. The group kidnapped and beheaded American hostage Nicholas Berg in May and is suspected in many high-profile attacks across Iraq during the past 17 months, including Tuesday's car bombing near a Baghdad police station that killed dozens of Iraqis applying for jobs.
U.S. officials have placed a $25 million bounty on al-Zarqawi's head.
The gunman warned they would behead hostages within 48 hours unless female prisoners were freed from Abu Ghraib prison northwest of the capital and Camp Bucca in Umm Qasr in the south.
Both are American-run facilities and Abu Ghraib is embroiled in a scandal over U.S. troops humiliating male Iraqi prisoners.
''By God, they will have their throats slit and their necks cut to serve as an example,'' the gunman said in Arabic.
But the kidnappers' demands confused Iraqi officials, who denied women were being held at either facility. An Iraqi Ministry of Human Rights official said that the only two female prisoners in U.S. custody are from Saddam Hussein's regime. Neither is at Abu Ghraib or Camp Bucca, the official said.
The video was the first word on the three Westerners' fate since they were snatched in a brazen raid on their home in the al Mansour district of Baghdad before dawn Thursday. The three work for ASCS/GSCS, a construction and services company based in Abu Dhabi, in the United Arab Emirates, Iraqi police said.
American and British Embassy officials and the men's employer could not be reached for comment Saturday.
Five other Western hostages are still missing - two French journalists, two Italian aid workers and an Iraqi-American businessman.
Meanwhile in western Anbar province, residents on Saturday discovered the body of their kidnapped deputy governor.
Assaults in and around Baghdad continued at a frenetic pace Saturday. Aside from the airport bombings, in central Baghdad, a roadside bomb killed an Iraqi and wounded two others in a car, while in Baqouba, a mortar shell outside a technical school wounded 11 students who had come to collect test scores.
Iraqi police also said one of their lieutenants and the director of a local office of the Human Rights Ministry were felled by assassins' bullets.