Egypt’s chief prosecutor has ordered an investigation into allegations that opposition leaders committed treason by inciting supporters to overthrow Islamist President Mohamed Morsy.

The probe by the President-appointed prosecutor Talaat Abdullah was launched a day after Mr. Morsy 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.

The probe was almost certain to sour the already tense political atmosphere.

The allegations were made initially in a complaint by at least two lawyers sent to the chief prosecutor earlier this month. They targeted opposition leaders Mohamed ElBaradei, a Nobel Peace laureate and former head of the U.N. nuclear agency IAEA; former Foreign Minister Amr Moussa and Hamdeen Sabahi. Both Mr. Moussa and Mr. Sabahi were presidential candidates who competed with Mr. Morsy in the last election.

There was no immediate comment by any of the three leaders named but the opposition dismissed the allegations.

Emad Abu Ghazi, secretary-general of the opposition party Mr. ElBaradei heads, said the investigation was “an indication of a tendency toward a police state and the attempt to eliminate political opponents”.

The investigation does not necessarily mean charges will be filed against the leaders. But it is unusual for state prosecutors to investigate such broad charges against high-profile figures.

In an apparent protest against the decision to keep the same Prime Minister, the minister of parliamentary affairs resigned. A member of his Islamist party said Prime Minister Hesham Kandil has not lived up to the challenges of the previous period, and a stronger, more political Prime Minister should be nominated.

Details of the complaint filed by the two lawyers were carried on the website of Mr. Morsi’s Muslim Brotherhood.

The report said their complaint alleged that the opposition leaders were “duping simple Egyptians to rise against legitimacy and were inciting against the President”, which constitutes treason.

The Nov. 22 presidential decrees appointed Mr. Abdullah to replace the chief prosecutor who was a holdover from the Mubarak regime. The judiciary protested the move, seeing it as trampling of its authority to choose the chief prosecutor.

The Supreme Judicial Council, the country’s highest judicial authority, asked Mr. Abdullah to step down on Wednesday because he was appointed by the President.

Mr. Abdullah asked a judge to conduct the investigation, the state news agency reported.

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