Egyptian President Mohammed Mursi warned Sunday of taking unspecified measures to “protect the nation” following violent clashes two days earlier between opposition demonstrators and Muslim Brotherhood supporters in Cairo.

“I am president of all Egyptians and I will not allow anyone to tamper with the nation,” President Mursi said in statement posted on Twitter, adding: “If I am obliged to do what is necessary to protect this nation, I will do, and I fear I am about to do that.”

On Friday an office branch of the Brotherhood in Cairo was torched and ransacked in the clashes, while the Justice and Freedom Party (JFP) building in Alexandria was also looted. The party is the political arm of the Muslim Brotherhood.

Opposition activists had called for the protest a week after they battled with the Islamists near the same building in Cairo. The movement vowed on Thursday it would protect its headquarters and bused in hundreds of supporters.

“I urge all to maintain order and keep calm, and I repeat that the right to peaceful demonstration is guaranteed to all,” Mursi said.

The Islamist president added that the “law must be applied when the security of the nation is in danger.” He accused opposition media of inciting violence and warned of punishment.

“Some people are using the media to incite violence, and whoever is found involved will not escape punishment. Whoever participates in incitement is a participant in crime,” he said.

He said, “the attempts that seek to portray the country as a weak state are failed attempts [because] the state institutions are recovering and are able to deter anyone who oversteps the law.”

The Brotherhood has seen about 30 of its offices across the country attacked in widespread protests against President Mursi, the Islamists’ successful candidate in last June’s election.