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 Qaeda 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 homicide 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 Qaeda and other extremists.

In January 2008, suspected Al Qaeda militants opened fire on a convoy of tourists in Hadramut, killing two Belgian tourists and their Yemeni driver. A suicide bomber detonated his car among tourists at an ancient temple in central Yemen in July 2007, killing eight Spaniards and two Yemenis.

Militants in Yemen have also targeted foreign diplomatic and military targets in the country. A half dozen gunmen and two vehicles packed with explosives attacked the U.S. Embassy in the Yemeni capital, San'a, in September, killing 16 people, including six militants. Yemen was also the site of the 2000 bombing of the USS Cole that killed 17 American sailors.

Yemen was a haven for Islamists from across the Arab world during the 1990s, but after the Sept. 11 attacks, its government declared support for the U.S. campaign against international terrorism.

But its crackdown on militants has suffered a number of setbacks, such as the February 2006 prison breakout of 23 convicts — some of whom had been jailed for Al Qaeda-linked crimes. The country also has a weak central government and a powerful tribal system that leaves large lawless areas open for terrorist training and operations.