Eleven Islamist political parties launched the 'National Alliance for Legitimacy Support' on Thursday to "protect the Egyptian people's democratic gains."  The announcement comes one day before mass rallies planned in Cairo to support President Mohamed Morsi's rule.

The alliance – which was officially announced in a press conference at Cairo's International Conference Centre – includes the Freedom and Justice Party (the party from which Morsi hails), the centrist Al-Wasat Party, the Salafist Al-Watan Party, and the Building and Development Party of the ultra-conservative Al-Gamaa Al-Islamiya group.

The alliance also includes the Professional Syndicates Union, made up of 24 syndicates, and tribal coalitions from Sinai, Upper Egypt and the north coast city of Marsa Matrouh.

During the press conference, the alliance stated that it will coordinate efforts to "protect the choices of the Egyptian people." It will also hold demonstrations across Egypt to "denounce violence, resist thuggery and continue the people's revolution... using peaceful and legal means."

The alliance was announced ahead of anticipated nationwide protests on Sunday 30 June which will call for Morsi's resignation in addition to early presidential elections. The call for protests was first made by the Rebel movement, a campaign which aims to collect 15 million signatures withdrawing confidence from Morsi.

The opposition protests have been challenged by Morsi supporters, who cite Morsi's "constitutional legitimacy" to continue his presidential term until 2016.

Hundreds of thousands staged a rally at Rabaa Al-Adawiya Mosque in Cairo's Nasr City last Friday in support of Morsi. They are due to hold a similar rally this Friday which will be open-ended.

Tensions have been building between opponents and supporters of the president after clashes in several governorates – including Daqahliya, Sharqiya and Zagazig – left three dead and scores injured in the past week.

A three-hour speech by the president on Wednesday night offered limited concessions and called for national reconciliation but was not well-received by the opposition.  

The president's opponents have started preparations for next week's protests, erecting around 32 tents in Tahrir square on Thursday.