CAIRO — Mexico’s foreign minister traveled to Egypt on Tuesday to demand answers about a mistaken military airstrike over the weekend that hit a picnic full of Mexican tourists, killing a dozen people, while her Egyptian counterpart defended the professionalism and sacrifice of the Egyptian security forces.

The back and forth raised new doubts about the likelihood of a solution to the mystery of how an Apache military helicopter crew could have mistaken a midday picnic in the desert for a camp of heavily armed militants. Human rights advocates charged that the Egyptian Army had often failed to distinguish civilians from combatants and had seldom sought to investigate or punish those responsible.

“We are dealing with a dreadful loss of life and an unjustified aggression,” the Mexican foreign minister, Claudia Ruiz Massieu, said late Monday before boarding a plane with the families of those killed or injured for a hastily planned trip to Cairo.

She vowed to press the Egyptian authorities “for firsthand information that clarifies the circumstances of this deplorable event that cost the lives of innocent Mexican tourists.”