Egypt's opposition said on Sunday that it will appeal the results of a referendum that ruling Islamists said approved a new constitution, claiming that voting was riddled with "fraud and violations".

The announcement was made by the opposition National Salvation Front the day after the second and final round of the referendum that President Mohamed Morsi's Muslim Brotherhood said passed with 64 percent support, according to unofficial early tallies.

"The referendum is not the end of the road. It is only one battle," said the statement, read by Front member Abdel Ghaffer Shokr at a Cairo news conference. "We will continue the fight for the Egyptian people."

Another Front member, Amr Hamzawy, said: "We are asking the (electoral) commission to investigate the irregularities before announcing official results."

The results had been due to be announced on Monday.

"Our struggle is peaceful to bring down an invalid constitution" by having the commission recognise the alleged fraud and low turnout, Hamzawy said.

Opposition to the new constitution, drafted by an Islamist-dominated panel, fuelled weeks of protests in the run-up to the vote.

Some of them degenerated into clashes between rival demonstrators, including on December 5 outside the presidential palace in Cairo, when eight people were killed and more than 600 injured.

Morsi and Islamists backing the charter say it is necessary to restore stability after the early 2011 revolution that toppled Hosni Mubarak.

But the opposition sees the new constitution as a wedge to usher in creeping Islamic law through a weakening of human rights, particularly women's rights, and undermine the independence of the judiciary.