Survivors said their group was bombed from a plane and helicopters. As members of the tourist convoy tried to flee, additional forces on the ground fired on them, Egyptian security sources said.
Egypt's interior ministry described the attack in the country's western desert as an accident.
Mexico's President Enrique Pena Nieto said two Mexicans were killed in Sunday's incident, though Egyptian security and judicial sources later said eight Mexicans and four Egyptians were killed. The sources added that eight Mexicans and two Egyptians were wounded.
The sister of a Mexican Reiki healer who said her brother was among the dead said a relative of the group's tour guide had sent her a list of eight Mexicans killed in the attack.
Follow Larry Elder on Twitter
"Like" Larry Elder on Facebook