The Muslim Brotherhood's Freedom and Justice Party has called for a boycott of the upcoming constitution referendum.

"The Freedom and Justice Party calls on the free Egyptian people to boycott this so-called referendum. This null and void charter was drafted by a minority and is designed to give immunity to murderers who led a bloody military coup that was an insult to the dignity and will of Egyptians," it said in a statement on Wednesday.

The referendum, called by interim president Adly Mansour for 14 and 15 January , will be the first milestone in the transitional roadmap since Morsi, the country's first freely elected president, was ousted on 3 July following mass protests against his rule.

The draft, an amended version of the constitution passed in a referendum under Morsi in December 2012, was prepared by a mostly non-Islamist 50-member committee appointed by Mansour in September.

Interim president Mansour has called on those who opposed the road map set by the interim government on 3 July to "give up on their stubbornness," to "stop "following a mirage," and to "join the nation."

Most of the country's non-Islamist Egyptian parties, including the liberal Constitution Party, the Egyptian Social Democratic Party and leftist Tagammu, announced they will participate in the upcoming poll. 

Earlier this week, the ultra-conservative Salafist El-Nour party, a onetime ally of the Brotherhood's former ally which had one representative in the 50-member committee, announced it will campaign for a Yes vote.

"The military coup has defiled the legitimate constitution that was approved by a two-thirds majority and has produced an abomination instead," the statement said. "It is driving people to vote yes in exceptional circumstances and making them give up their rights and those of future generations."

The party said it would continue its "peaceful revolutionary escalation against the military coup."

Earlier this week, the National Alliance to Support Legitimacy, a Brotherhood-led pro-Morsi coalition, released a statement saying it was still undecided on whether to boycott the poll, because participation could be interpreted as an acknowledgement of the interim government's legitimacy.

Supporters of ousted president Mohamed Morsi continue to defy a fierce crackdown on the Brotherhood and its top leaders with daily marches against the military and the killing of hundreds of pro-Morsi protesters at sit-ins in August.