Shibam is one of Yemen's biggest tourist attractions
Four South Korean tourists visiting Yemen have been killed by an explosion while posing for photographs near the historic fortified city of Shibam.
Two Yemenis accompanying the party to a hill overlooking the UN World Heritage site were also killed. At least three other people were injured.
The cause of the blast is unclear although Yemen has been seen as a haven for Islamist militants.
Militants are known to have a presence in the surrounding province, Hadramaut.
The website of Yemen's governing party described the blast as a terrorist attack.
But a local security official told the Reuters news agency that Sunday's incident may have been the work of terrorists but could also have been due to the remnants of dynamite from a mine.
Shibam, with its 16th Century mud-brick buildings, is dubbed the "Manhattan of the Desert".
Islamist militants in Hadramaut have in the past year clashed with the Yemeni security forces on a number of occasions.
Yemen is one of the poorest countries outside Africa and there have been a series of previous attacks against Westerners, correspondents say.
A double car bomb attack on the US embassy in Yemen in September 2008, killed at least 16 people. It was the second attack on the embassy in six months.
In January 2008, two Belgian tourists were shot dead along with their guide and eight Spanish holidaymakers, plus two Yemeni drivers, died in a car bomb attack in July 2007.
Other previous attacks include the suicide bombing of the USS Cole in the port of Aden in 2000, which killed 17 US soldiers.
Last month, Yemen released 176 men suspected of ties to the militant network al-Qaeda on condition of good behaviour, officials said.