CAIRO -- A strong explosion rocked a security headquarters in downtown Cairo, and state television reported at least three people were killed and 35 injured.

The blast came on the eve of a holiday honoring the police.

Attacks against security forces are common in Egypt's restive Sinai Peninsula, but relatively rare in cities such as Cairo. A bombing at a security headquarters last month in the city of Mansoura, north of the capital, killed at least 15 people.

Friday, the main Muslim prayer day, is a weekend day in Egypt, so relatively few passersby were in the vicinity of the early-morning explosion, but officers were on duty inside the building.

Television showed images of the building's damaged facade, with debris and broken glass littering the ground.

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