Four South Korean tourists and their Yemeni guide have been killed in an explosion in southern Yemen, security officials say.

The blast at a tourist site in the southern province of Hadramut on Sunday also injured three other South Koreans.

There were conflicting reports about the nature of the bombing, with a security official telling The Associated Press that it was a suicide attack and another saying it was a roadside bomb detonated by remote control.

One official told the Reuters news agency that "maybe it was a terrorist attack but it could also be remnants of dynamite from a mine going off".

No group has claimed responsibility for the explosion and security sources have not accused any group.

But Khaled al-Hammadi, a journalist in Yemen's capital, Sanaa, told Al Jazeera that the attacks come after the announcement of new leadership for al-Qaeda in the Arabian peninsula.

"The Yemeni government has conducted a lot of operations to combat al-Qaeda's operations in the country with the co-operation of the international community, particularly the US government.

"There are currently a lot of [court] trials in which al-Qaeda members are accused," he said.

The blast occurred in the fortress town of Shibam a Unesco World Heritage site famous for its 16th century mud brick buildings that rise up to 16 storeys.

It happened as the tourists passed a vehicle at the entrance to Mahram Bilqis, an ancient oval-shaped temple celebrated for belonging to the Queen of Sheba, an official said.