"We've seen reports that potentially a US citizen was injured," Kirby told a daily briefing. "Our embassy in Cairo is making the appropriate inquiries with local police, and of course, they're monitoring it."

Pena Nieto said he had been assured Egypt's prime minister would personally spearhead a probe.

Alvarez said the survivors he visited in hospital had told him they had been bombed by helicopters and an aircraft while they stopped for a break in the desert. The tourists had arrived in Egypt on Sept. 11.

Reuters spoke to Araceli Rangel Davalos, whose nephew Rafael Bejarano, a Reiki healer and musician was killed. She said her sister Marisela was wounded. She said she knew the group's guide, an Egyptology expert whom she identified as Nabil Altawami, well. She had not yet spoken to her sister.

"I have travelled with the guide around 9 times, and he never exposed us to any danger," she told Reuters by telephone. "He protected us."

Gabriela Bejarano, Rafael's sister, cast doubt on the Egyptian government's account of the incident.

"I don't think they were mistaken (for militants)," she told local radio in Mexico. "As far as I understand ... they were dining when they came under attack ... They were in a permitted area. On this occasion they didn't stay to camp, because that was what was not permitted."

Egypt's ambassador to Mexico, Yasser Shaban, said he assured Mexico's government Egypt was taking the incident very seriously and was committed to establishing exactly what happened.