Thousands of protesters are holding rallies across Egypt to demand the reinstatement of ousted president Mohammed Morsi.

The Muslim Brotherhood, from which Mr Morsi hails, was mobilising followers to march in Cairo and elsewhere for a protest they dubbed "breaking the coup".

Youth activists who launched the massive protests that led to Mr Morsi's ousting by the military also plan a mass demonstration in Cairo's Tahrir Square, raising fears of clashes in the capital between the two sides and authorities.

The military has warned it will act swiftly to prevent violence.

The protests come days after an interim administration was appointed.

Egypt's interim president, Adly Mansour, has pledged to protect his country against those who seek chaos and violence in the aftermath of the popularly backed military coup. He gave his first address to the nation ahead of the protests.

Egypt's military, already worried by post-coup violence that has killed more than 60 people, issued a stern warning about causing unrest during the scheduled protests.

In his eight-minute, pre-recorded message broadcast on state television, Mr Mansour said Egypt was going through a "decisive period" in its history where some wanted to drag the country towards the "unknown" and cause chaos.

"They want this period to be an introduction to violence and blood, and we want it to establish for the concept of protecting lives and human rights," Mr Mansour said.

He did not name those who he said "are pushing the nation towards the abyss thinking they are doing good" - but clearly was referring to pro-Morsi protesters. He said those who protested against Mr Morsi starting on June 30 were "the genuine owners of legitimacy".

Mr Mansour said his government was committed to realising security and stability and would not be "scared or terrorised". And he vowed not to be "lenient with those who kill the innocents".

"We will go through the battle for security to the end. We will preserve the revolution," he said. "History will not turn around."

Mr Mansour said justice and reconciliation would be "for all, without exclusion or exception", suggesting that the process would include Islamists and former regime officials.

A senior Brotherhood official and former politician, Saad Emara, said after the speech that his group did not recognise Mr Mansour as the country's leader. Mr Emara called Mr Mansour merely a representative of General Abdel-Fattah el-Sissi, the nation's army chief.

Mr Mansour's speech is a sign that he and the interim administration are nervous of any opposition on the street, Mr Emara said.

"There is a contradiction in his speech between the threats and the call for reconciliation," Mr Emara said. "They want to turn this page."