President Abdel-Fattah el-Sissi did not go into specifics in an address broadcast live, saying only that he would "remove from the face of the Earth" anyone plotting to bring down the state.
In recent weeks, Egypt has seen startlingly public shows of anger over police abuses and brutality.
Rights groups have documented arbitrary arrests, torture and disappearances.
Even stalwartly pro-government TV commentators have raised alarm over a series of perceived miscarriages of justice, police brutality and economic problems - a shift from the near blanket avoidance of criticism in the past two years.
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"Please, don't listen to anyone but me. I am dead serious," he said sharply.
"Be careful. No one should abuse my patience and good manners to bring down the state."
"I swear by God that anyone who comes near it, I will remove him from the face of the Earth," he said, then added, seeming to address those conspiring against the state, "What do you think you're doing? Who are you?"
It is "still very early for open democratic practices, like criticizing and pushing (officials) out of office," he said, adding that democracy is being practiced but "under difficult circumstances, so let us safeguard Egypt."
El-Sissi was elected president a year later in a landslide.
Supporters largely cheered his government's crackdown on Islamists - jailing thousands and killing hundreds - and the arrests of dozens of secular activists, including leaders of the 2011 uprising.
El-Sissi devoted much of his 120-minute speech, his longest since coming to office in June 2014, to the threats Egypt faces and his efforts to spare it from the violence convulsing much of the region.
"What has been achieved in the last year and half was not achieved in 20 years before then," he said, referring to a series of infrastructure projects, including an expansion of the Suez Canal.