Gunmen kidnapped two American tourists and their driver in Yemen on Monday and demanded the release of a jailed tribesman, security officials said.
The U.S. Embassy in San'a said it was working with Yemeni authorities to resolve the situation, and a U.S. official in Washington said it did not appear to be an act of terrorism.
The security officials and members of the kidnappers' tribe said the two Americans -- a man and a woman -- were seized while traveling to 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.
Relatives of the Americans' taxi driver, Mohammed Saleh, said he phoned after the kidnapping to report that six gunmen stopped them on the road and took them to the al-Hamra village.
Members of the kidnappers' Sharda tribe said the hostages were now their "guests."
The driver's relatives and the tribesmen spoke on condition of anonymity to avoid trouble from the authorities.
The security officials said the American tourists arrived in Yemen Saturday on a flight from Dubai.
Kidnappings are frequent in Yemen and are usually carried out by disgruntled tribesmen hoping to win concessions from the government. In most of those cases, the captives are freed unharmed. In the past few years, however, al-Qaida has begun kidnapping foreigners as well, sometimes with lethal results.
They often take place outside the heavily guarded capital, underlining the fragility of security in rural areas. It is this weak government authority outside San'a that's allowed al-Qaida militants to seek refuge in the impoverished Arab nation in the southern corner of the Arabian Peninsula, thus posing a threat to the interests of the West and its allies in a strategic part of the Middle East.
The U.S. State Department said Monday's kidnapping was apparently not an act of terrorism.
"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," spokesman P.J. Crowley said. "So we have every reason to believe that this is one of those cases."
The United States and other Western powers have been increasing their support to Yemen's security forces to enable them to better deal with the al-Qaida threat. However, such efforts are often frustrated by the protection offered by tribal chiefs to the militants, the country's difficult mountainous terrain and the deep anti-Western sentiments shared by many Yemenis.
Three members of Sharda tribe said the kidnappers have moved the Americans and their driver to a rugged mountainous area, away from the main road. The two were visiting the Haraz area, a tourist destination known for its green hills and coffee plantations, when they were kidnapped while driving down the main road.
The tribesmen, who spoke to a reporter in Hayma, nearly 25 miles (40 kilometers) from where the tourists were snatched, said gunmen are guarding the area to repel any advances by the government's security forces. They spoke on condition of anonymity for fear of retribution.