Egypt's interior ministry said Sunday it had broken up a "military wing" of the Muslim Brotherhood, which it said was formed to attack policemen, AFP reports.
The announcement is the most detailed accusation yet implicating the group in terrorist attacks.
The interior ministry said it uncovered a cell organized by a Brotherhood leader that killed five policemen in an attack on a checkpoint south of Cairo last month.
If the accusation is true, it would confirm suspicions some Brotherhood members are joining a growing militant campaign amid a massive crackdown on the Islamists.
"Information showed that leaders of the terrorist Muslim Brotherhood instructed a member of the administrative office... to form a military wing," the statement said, according to AFP.
Scores of policemen and soldiers have been killed in bombings and shootings since the Egyptian army ousted the Muslim Brotherhood’s president, Mohammed Morsi, in July.
The interior ministry said police have arrested five suspects in the Brotherhood "military wing" so far, including a young man shown on state television confessing his involvement in the January 23 attack on the checkpoint.
The ministry identified him as the son of a Muslim Brotherhood leader.
More than 1,400 people have died in street clashes, and thousands have been imprisoned, in the crackdown on Morsi's supporters following his overthrow in July.
The Egyptian army has been busy with a military offensive against Sinai-based terrorists. On Saturday, the army said that it killed 16 Islamist terrorists in the Sinai, near the border with Gaza, the day before.
The liquidation of the 16 terrorists was conducted by an Egyptian airstrike in an area south of Sheikh Zuweid, according to the army's statement.
The army has also already been cracking down on Hamas, the Muslim Brotherhood’s offshoot which controls Gaza and is seen by Egypt as a threat to its security. Egypt has been shutting down Hamas tunnels which lead from the Sinai into Gaza. Hamas uses these tunnels to transfer goods, weapons and even terrorists.
Egypt has also blamed Hamas of being involved in teaching Islamists in Egypt how to carry out attacks. Hamas has denied the allegations.
Egyptian officials indicated last month that the military plans to take on Hamas in Gaza, mostly by working with Hamas's political rival Fatah and supporting popular anti-Hamas activities in the region.