The Cairo-based Al-Azhar, Sunni Islam's top authority, voiced concern on Monday about the infiltration of gunmen into "peaceful" protests across Egypt demanding the resignation of Islamist President Mohamed Morsi.

"Al-Azhar is monitoring with deep concern what is happening, particularly reports of casualties and the arrest of arms smugglers who seem to have infiltrated the peaceful scene in a bid to turn their weapons on gatherings and cause further bloodshed," a statement said.

It came after at least 16 people died across Egypt on Sunday in clashes between supporters and opponents of Morsi.

"Al-Azhar cannot ignore what is happening or stand with arms folded as these groups infiltrate the ranks of peaceful protesters, carrying all sorts of weapons in order to drag the country into confrontations which will lead God only knows where," the statement said.

The top Sunni authority urged all relevant state institutions "to take immediate measures to disarm and arrest these people," and and called on everyone to show restraint.