The US embassy in Cairo on Friday warned US nationals in Egypt to exercise caution and avoid visiting the Giza Pyramids.
The message, sent via email, noted that the embassy had become aware of an increasing number of incidents of 'criminal conduct' in and around Egypt's Giza Plateau area.
It cited one recent case in particular in which unidentified individuals had pounded on the doors of a car carrying tourists, which they had attempted to open by force.
"US citizens should elevate their situational awareness when travelling to the Pyramids, avoid any late evening or night travel, utilise a recommended or trusted guide and closely guard valuables," the embassy warned.
It went on to state that a lack of adequate security in the area had heightened fears of possible violence.
Such security warnings are frequently issued to citizens by US embassies around the world.
The latest warning comes at a sensitive time for Egypt, when the local tourism industry is already suffering from months of post-revolution political unrest.