Egypt on Thursday warned users of social media such as Facebook and Twitter of arrests if they incited violence through their posts, saying they were being tracked.
The interior ministry said 10 members of the "terrorist (Muslim) Brotherhood" had already been arrested for such acts.
The authorities were using "modern technology to track" those inciting violence against police and civilians, and for posting information on how to make explosives.
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Since the ouster of Islamist president Mohamed Morsi by the army in July, the new military-installed authorities have cracked down on his supporters and the Muslim Brotherhood.
The crackdown has also targeted several liberal activists, with some of the symbols of the 2011 uprising against president Hosni Mubarak finding themselves behind bars.
During the anti-Mubarak revolt, Egyptians were active on social networks Facebook and Twitter to mobilise people for mass street protests against the former strongman's regime.
In December, Egyptian authorities designated the Brotherhood to which Morsi belonged a "terrorist organisation" after accusing it of a deadly car bombing against a police building north of Cairo.
Egypt has been rocked by deadly bombings and attacks on security forces, mostly in the restive Sinai Peninsula where Islamist militants are active but also in other regions, including Cairo.