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.