Egypt's largest Islamist coalition has called on supporters of ousted president Mohamed Morsi to escalate protests during the country's two-day presidential polls next week, scheduled for 26-27 May.

In a statement released on Thursday under the slogan "Boycott the Presidency of Bloodshed", the National Alliance to Support Legitimacy (NASL) described the upcoming presidential elections as a "comic play".

The alliance also announced that it will be displaying pictures of the "legitimate president" Morsi – elected in June 2012 and then deposed by the army a year later – and other political Islamist figures who have been detained nationwide since Morsi's ouster.

Egyptians abroad wrapped up voting earlier this week, with nearly 95 percent of the 318,033 votes cast going to former military chief Abdel-Fattah El-Sisi. His challenger, Nasserist candidate Hamdeen Sabahi, secured just 5.4 percent of the expat voting.

In its statement on Thursday, the pro-Morsi alliance declared the expat voting to be void and stressed the low turnout. Expat voting during the 2012 presidential elections that brought Morsi to power saw participation from 311,875 out of 586,803 registered voters.

The Muslim Brotherhood-led coalition insists Morsi is Egypt's legitimate president. The group describes Morsi – who currently faces multiple trials on charges including murder and espionage – as the "kidnapped president".

El-Sisi, as the country's defence minister, led Morsi's removal, following mass protests against the Islamist president's troubled one-year rule.

Despite the dwindling numbers of Morsi supporters in street protests – now mainly confined to some Egyptian universities – the NASL consistently claims the momentum of its demonstrations remains undeterred.