Spokesman P.J. Crowley said the two, who were not identified, were snatched Monday and that U.S. officials are working with local authorities to attempt to gain their release.
"There has been unfortunately a bit of a side business in what are called 'tourist kidnappings' where, for whatever reason, a certain tribe has a particular grievance with the (Yemeni) government and uses the presence of foreigners for leverage," Crowley said. "So we have every reason to believe that this is one of those cases."
In the past few years, the al-Qaida terrorist network also has kidnapped foreigners in Yemen for its own reasons.
In Yemen, officials said Monday's kidnap victims were a man and a woman. They were seized while traveling in al-Hudaydah province west of the capital, San'a. The officials spoke on condition of anonymity because they were not authorized to speak to the media.
Taxi driver Mohammed Saleh, who was driving the two, said six gunmen stopped them on the road and took them to the al-Hamra village. Al-Sharda tribesmen said the hostages were now "guests" in the village.
Associated Press writer Ahmed Al-Haj contributed to this report.