An explosion targeting a tourist bus injured at least 12 people near a new museum being built close to the Giza pyramids in Egypt on Sunday, two security sources said.

Most of those injured were foreign tourists, the sources said. There were no reports of deaths.

The U.S. embassy in Cairo said it was aware of the incident. "We are not aware of any injuries to U.S. citizens at this time," it said in a statement.

There was no immediate word on whether any U.S. citizens were on the bus at the time of the blast.

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A witness, Mohamed el-Mandouh, told Reuters he heard a "very loud explosion" while sitting in traffic near the site of the blast.

Pictures posted on social media showed a bus with some of its windows blown out or shattered, and debris in the road next to a low wall with a hole in it.

The attack comes as Egypt's vital tourism industry is showing signs of recovery after years in the doldrums because of the political turmoil and violence that followed a 2011 uprising that toppled former leader Hosni Mubarak.

It is the second to target foreign tourists near the famed pyramids in less than six months.