Egypt’s chief prosecutor ordered an investigation on Thursday into allegations that opposition leaders committed treason by inciting supporters to overthrow Islamist President Mohammed Morsi.

The probe by a Morsi-appointed prosecutor was launched a day after the president called for a dialogue with the opposition to heal rifts opened in the bitter fight over an Islamist-drafted constitution just approved in a referendum. The opposition decried the investigation as a throwback to Hosni Mubarak’s regime, when the law was used to smear and silence opponents.