The Rabaa al-Adawiya Square sit-in organizers announced on Sunday foiling an attack by army and police forces on the square, claiming the purpose was to "kidnap" some of the sit-in leaders and destroy the radio broadcast station.
"They wanted to create a state of confusion in the square and use it as a cover to kidnap some of the sit-in leaders and hit the radio broadcast station," charged Mohamed el-Beltagui, a senior Muslim Brotherhood figure.
Safwat Hegazi, a senior figure of the National Alliance for the Defense of Legitimacy, a coalition of largely Islamist parties and figures supportive of ousted President Mohamed Morsi, said army and police armored vehicles tried to storm the square from Tayaran and Nasr streets but failed.
There was no immediate comment from army or police officials on the accusations.
Supporters of Morsi have been staging daily mass demonstrations and sit-ins nationwide since his ouster by the army on July 3 following mass protests against him.
Rabaa al-Adawiya is their main sit-in site and has been continuing for 39 days.
On Wednesday, the government described the sit-ins as a threat to national security and that the Interior Ministry had been mandated to take all necessary measures to disperse them.