Six people were injured on Wednesday morning when security forces attempted to defuse a bomb placed under a bridge in Fayoum, Al-Ahram Arabic news website reported.
Security forces were spraying water cannons at the bomb when it exploded, injuring four policemen and two civilians, and causing damage to nearby shops.
One of the injured was referred to intensive care with a brain hemorrhage after being struck in the head with shrapnel.
The five other injured received treatment but their injuries are not thought to be serious.
Fayoum is 100km south of the capital, Cairo.
In recent months, dozens of small bombs have been planted by alleged Islamist militants, targeting security personnel as well as economic installations such as electricity pylons and mobile phone stores.