A bomb killed four South Korean tourists and their local guide in Yemen on Sunday, officials said, the latest such attack targeting foreigners visiting this poor Arab country that has both famed historic sites and a strong al-Qaida presence. The attack occurred as the tourists were posing for photographs near the ancient fortress city of Shibam - a UNESCO World Heritage site known as "the Manhattan of the desert" because of its towering 16th century mud brick buildings - said Yemeni security officials.

There were conflicting reports about the nature of the bombing, with one security official saying it was a suicide attack and another saying it was a roadside bomb detonated by remote control. They spoke on condition of anonymity because they were not authorized to talk to the media.

A South Korean Foreign Ministry official confirmed the tourists were killed in the attack. He spoke on condition of anonymity in line with ministry policy. The Yemeni Ministry of Tourism said the dead South Koreans included two men and two women. Their Yemeni guide was also killed in the attack, which wounded four other foreigners and an unspecified number of Yemenis, said the ministry's statement.

The city of Shibam in Yemen's southern Hadramut province is one of the country's most prized tourist sites. The ministry said it was not canceling any tours in the country and has stepped up security for all other tourist groups.

This impoverished country on the southern tip of the Arabian peninsula is Osama bin Laden's ancestral homeland and has long been a center of militant activity despite government efforts to fight al-Qaida and other extremists.