“It resulted from the explosion of a charge prepared in basic way containing gunpowder and nails,” Magdi Radi told Reuters.
“It is probable that the one who has yet to be identified was the source of the explosion,” he said.
The blast, outside a perfume shop near the al-Azhar mosque, injured 16 others – nine Egyptians, four Americans and three French nationals.
The injured were taken to the nearby Al-Hussein hospital, which was cordoned off by armed Egyptian security forces.
The explosion happened in the el-Hussein area of medieval Cairo at about 5:45 pm, leaving behind a two metre wide crater.
Thousands of tourists pass through the nearby al-Moski bazaar every day, buying souvenirs from stalls that line the area’s maze of medieval alleyways.
There was no immediate claim of responsibility for the blast.
The US Embassy in Cairo said was no independent information to suggest it was part of a wider campaign, but warned its citizens to stay away from tourist areas of the city.
It’s the first attack in the Egyptian capital in seven years and comes amid unprecedented internal political upheaval.
In recent weeks the country has witnessed unprecedented demonstrations, campaigning for the lifting of the 24-year-old state of emergency and constitutional and political reforms.
In October last year, at least 34 people, including several Israeli tourists, were killed in triple bomb attacks on the Hilton hotel Taba and two nearby resorts in the Sinai Peninsula.
The Taba attack was the worst on tourists in Egypt since 1997 when 58 foreign holidaymakers were killed in a attack in the southern city of Luxor.