An Egyptian party led by a prominent Islamist says it will boycott the referendum on the country's draft constitution after several of its members were arrested for campaigning against the charter.

Monday's statement by the Strong Egypt party of Abdel-Moneim Abolfotoh came on the eve of the voting on the amended charter.

The two-day referendum offers the country's interim, military-backed government its first electoral test since the ouster of Islamist President Mohammed Morsi in a coup last July.

Morsi's Brotherhood, which has since been branded as a terrorist group, has called for a boycott of the vote as well.

The charter is an overhaul of an Islamist-backed constitution adopted in December 2012 under Morsi. While decreasing the role of Islamic Shariah in legislation, the charter consolidates the military's powers.