Most of those injured were foreign tourists, the sources said. One security source said they included South African nationals.

There were no reports of deaths. 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.

In December, three Vietnamese tourists and an Egyptian guide were killed and at least 10 others injured when a roadside bomb hit their tour bus less than 4 kilometres (2.5 miles) from the Giza pyramids.