CAIRO — Egypt's president warns he may be about to take measures he did not specify to "protect this nation."

Mohammed Morsi's warning came in a series of tweets posted on Sunday, two days after violent clashes between supporters of his Muslim Brotherhood and opposition protesters in Cairo. At least 200 people have been injured, some seriously, outside the Cairo headquarters of the Brotherhood, Egypt's most dominant political group.

An Islamist elected in June, Morsi also warned that "appropriate measures" would be taken against politicians found to be behind Friday's violence, regardless of their seniority. Anyone found to be using the media to "incite violence" will also be held accountable, he added.

Friday's clashes followed an assault a week earlier by Brotherhood supporters on protesters painting hostile graffiti outside the group's headquarters.