Gunmen kidnapped two Americans and a Briton from a house in an affluent central Baghdad neighbourhood on Thursday, the latest in a nearly six-month campaign of abductions of foreigners in Iraq.
Militants posted video footage on the Internet purportedly showing the killing of three Arabic-speaking truck drivers, who were also shown warning others against working for US forces in Iraq.
The US embassy named the two kidnapped Americans as Jack Hensley and Eugene Armstrong but did not give their home towns.
The British embassy said no details on the kidnapped Briton would be released until his family had been informed.
The trio worked for GSCS, a United Arab Emirates-based firm that has won building contracts in Iraq, the company said.
The men were staying in a two-storey building in the wealthy Mansur district when gunmen stormed the house at dawn.
An Interior Ministry spokesman said no shots were fired. Colonel Adnan Abdel-Rahman quoted witnesses as saying the men were bundled into a van and driven off.
The video footage of the three truck drivers, posted on a Web site which has previously carried militant statements, showed them standing with their hands tied behind their backs.
"My name is Abbas Nouri ... I advise truck drivers not to work with Americans or do such work," a dark-skinned man with a moustache said in Arabic.
The hazy footage later showed them lying face down on the floor with sounds of gunshots in the background and smoke.
The men's Arabic accents suggested they could have been Iraqis, Kurds or Jordanians.
"This video shows the confessions of three drivers who transported supplies to crusader military forces and shows the Mujahideen killing them," said a statement by the Army of Ansar al-Sunna militant group.
More than 100 foreigners have been seized since April. About two dozen have been killed but most have been freed. At least four Europeans are still held - two male French journalists seized last month and two Italian female aid workers.
A roadside bomb in Baghdad on Thursday killed a passer-by and wounded 16, and Iraqi security forces found and defused a car laden with 400 kg (880 lb) of explosives near the so-called Green Zone housing the interim government and US embassy.
A bomb south of Baghdad killed one person, and an oil pipeline was set ablaze near the town of Baquba, some 65 km (40 miles) north of the Iraqi capital.