Sanaa, Yemen (CNN) -- Four civilians were killed and three were injured Thursday when their vehicle was shelled in Yemen's southern Shabwa province, two Interior Ministry officials said.
Eyewitnesses told CNN that two of the injured are in serious condition.
The civilians are part of the powerful Awaliq tribe, which is demanding an explanation from the Yemeni government. Tribal leaders blame government forces from a nearby military base for the mistake attack.
"The shelling came from the direction of a military base, and militants don't have a presence in those areas," a witness said.
But a senior military official in Shabwa denied the military had anything to do with the shelling. "The army is trained and such a mistake is not possible," the official said.
He blamed terrorists for the attack, saying it was meant to cause friction between the Awaliq tribe and government forces.
Government troops have taken control of a number of districts previously held by al Qaeda militants.
Thursday's shelling came nearly a month after Yemen launched a military offensive against al Qaeda in the Arabian Peninsula amid an uptick in violence in the capital. Thousands of troops were deployed to the provinces of Hadramout, Shabwa, al-Baitha and Abyan.