"We call for the immediate and safe recovery of all hostages in Iraq, including the American citizen and the three Romanian journalists taken on Monday," said State Department spokesman Steve Pike.
Pike said he could not provide more information because the State Department did not have the US citizen's authorisation to do so.
Earlier, Aljazeera broadcast a video showing the three Romanian journalists and the US citizen sitting on the floor flanked on both sides by two men pointing machine guns at their heads.
The group who abducted the four would not identify itself.
One of the seized journalists, Marie Jeanne Ion, said no demand had so far been made by the abductors.
The journalists were kidnapped on Monday while on a short assignment to Iraq.
Ion and Sorin Miscoci work for Romania's Prima TV while Ovidiu Ohannesian represents Romania Libera newspaper.
Sunni speaker named
Meanwhile, following a stormy opening session of the Iraqi parliament, Sunni Arab political forces in Iraq have chosen Mashaan al-Jaburi as their candidate for the post of speaker in the country's interim National Assembly.
Media were asked to leave the
opening session on Wednesday
Al-Jiburi was nominated at a meeting attended by representatives of the Islamic Party, the Royal Constitution Movement, the Arab Democratic Party and Independent Democratic Party, among other Sunni political forces.
However, Aljazeera learned that some members of the 275-member parliament have voiced their concern over the choice of al-Jaburi.
The exact nature of their concerns were, however, not immediately known.