The United States mission in Cairo has condemned a blast that killed 12 people early on Tuesday.
"We support the Egyptian government's efforts to bring those responsible to justice," said a statement on the embassy's official website.
The embassy sent its deepest condolences to the families of the victims and wished the injured a quick recovery.
Twelve people were killed, including nine security personnel, and 134 were injured in a bomb blast at a security compound in the Nile Delta city of Mansoura in Dakahlyia in the early hours of Tuesday.
"These cowardly operations are carried out by a misguided faction that has deviated from the Egyptian national community and adopted violence and treachery," said the army.
Egypt's Prime Minister Hazem el-Beblawi released a statement shortly after the attack officially announcing the Muslim Brotherhood as a terrorist organization, but the group itself has condemned the attack.
Attacks on security forces and their offices have noticeably risen since the ouster of the Muslim Brotherhood's Mohamed Mursi from power.
Egypt's army ousted Mursi in July in response to mass demonstrations across the country against his rule, announced early presidential and parliamentary elections and suspended a 2012 constitution written by an Islamist-led assembly.
A new constitution will be voted on in a referendum early next year.