CAIRO (Reuters) - Egyptian authorities arrested three leading opposition figures on Thursday including a former senior diplomat who had called for a referendum on President Abdel Fattah al-Sisi’s government, security sources said.

No specific charges had yet been laid against the men, but they were arrested on the orders of Egypt’s public prosecutor, the sources said. Egypt’s interior ministry did not immediately respond to requests for comment.

Egyptian authorities have jailed thousands of Sisi opponents and critics in recent years, including alleged Islamist militants and secular rights activists. The government says its actions are directed at terrorists and saboteurs trying to undermine the state.

The ex-diplomat and former ambassador, Masoum Marzouk, earlier this month called for a referendum on Sisi’s government, questioning its popularity in rare public criticism.

He said the government’s term should end and parliament be dissolved if a majority of Egyptians gave it a vote of no confidence.

The other two men arrested were Raed Salama, a senior member of the opposition Dignity Party which Marzouk used to belong to, and academic Yahya Kazaz, who recently called for Sisi’s departure on his Facebook page, writing “resistance is the solution”.

Prior to Sisi’s landslide re-election in March - in a vote where he was the only serious candidate - challengers were jailed or pulled out of the race citing intimidation. Security forces also detained several journalists and online critics in May.

Sisi’s supporters say the crackdown on dissent is needed to stabilize Egypt after a 2011 uprising and the unrest that followed, including an Islamist insurgency in the Sinai Peninsula that has killed hundreds.

The former general became president in 2014, a year after he led the ouster of Islamist president Mohamed Mursi, Egypt’s first freely-elected head of state, after popular protests against his rule.

Mursi came to power after the 2011 uprising that toppled Hosni Mubarak who had been president for nearly 30 years.