SANAA - An explosion at a tourist site in southern Yemen killed four South Korean tourists and a Yemeni man on Sunday, a Yemeni security official said.

He said police were investigating the cause of the blast, which injured three other South Koreans, in the city of Shibam in the southeastern province of Hadramout.

"Maybe it was a terrorist attack but it could also be remnants of dynamite from a mine going off," the official told Reuters.

He said the explosion occurred as the tourists visited the city dubbed the "Manhattan of the desert" - a UNESCO World Heritage site famous for its 16th-century tower houses which were made with mud bricks and rise up to 16 storeys high.

In January 2008, two Belgian tourists were killed in Yemen in an attack blamed on al Qaeda-linked militants who have launched frequent attacks on government and Western targets, including the U.S. embassy, a U.S. warship and a French supertanker.

The Arabian Peninsula country, one of the poorest outside Africa, has been seen as a stronghold of Islamist militants.

In a separate development, authorities said they had arrested Abdullah al-Harbi, a Saudi man who was on a list of 85 suspected militants issued by Saudi Arabia in February.

The Saudi list was issued after al Qaeda's wing in Yemen, Osama bin Laden's ancestral home, issued a video on the Internet in which it changed its name to Al Qaeda in the Arabian Peninsula, in an apparent attempt to revive the Islamic militant group in Saudi Arabia.

The leader of the group, a Yemeni, appeared in the video aired in January and threatened attacks against Westerners in the region.

Insecurity has affected international companies developing Yemen's oil and gas sectors, while attacks on foreigners - including kidnappings by disgruntled tribesmen - may prove fatal for the nascent tourism industry, Western diplomats say. --REUTERS