An explosion rocked a busy square in central Cairo late Friday, killing one police officer and causing panic, Egypt's Interior Ministry and security officials said.
The ministry said the bomb detonated next to a traffic post in Lebanon Square in Cairo's Mohandessin district, killing Maj. Mohammed Gamal Eddin.
A security official said the bomb was planted inside the traffic post and it exploded around 10 p.m. Cairo time. A second official, however, said unidentified assailants hurled the bomb from a bridge over the traffic post before fleeing. It was not immediately possible to reconcile the two accounts.
Three other people were injured including a senior police officer, the two officials said, speaking on condition of anonymity because they were not authorized to speak to the press.
Security forces sealed off the area while searching for more bombs.
No group immediately claimed responsibility for the attack.
Egypt has been hit with violence since the military overthrow of Islamist President Mohammed Morsi last year.
Since then, the country's military-backed interim government has stepped up its crackdown on Morsi's group, the Muslim Brotherhood, and followers who hold near-daily street demonstrations denouncing his ouster and the subsequent killings of hundreds of supporters. The protests frequently descend into violence, and ongoing street battles with security forces fuel unrest.
An al-Qaida-inspired group, Champions of Jerusalem, has claimed responsibility for most of the deadly attacks, including car bombs and the assassination attempt of Egypt's interior minister last year.
The government has blamed the violence on Morsi's group and branded it a terrorist organization. The group denies it and says it is abiding by peaceful means, including protests.
New groups have emerged over the past few months seeking revenge from security forces for killings of pro-Morsi protesters, including one called Ajnad Misr, Arabic for "Egypt's Soldiers." The group claimed responsibility for several small bombings, including three blasts earlier this month outside a university campus in central Cairo that killed one senior police officer and injured five others.
More than 430 police officers and army personnel have been killed in terrorist attacks since mass demonstrations against Morsi on June 30, according to government figures.
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