The health ministry said the death toll from nationwide violence in Egypt has climbed to 578, making it the bloodiest day since the Arab Spring in 2011 toppled longtime President Hosni Mubarak in a popular uprising.
In Cairo, the march set out from the Al-Iman mosque, where dozens of corpses of protesters clad in white shrouds were lined up before grieving relatives.
"The interior ministry has instructed all forces to use live ammunition to counter any attacks on government buildings or forces," the ministry said in a statement today.
There were also reports of clashes in Ma'adi, a neighbourhood in southern Cairo, between local residents and Morsi supporters, with witnesses saying both sides exchanged gunfire.
More From This Section
In a separate statement, the cabinet accused Morsi's Muslim Brotherhood of committing acts of "terrorism and vandalism".
"We will always be non-violent and peaceful. We remain strong, defiant and resolved," Brotherhood spokesman Gehad El-Haddad wrote on his Twitter feed.
"We will push (forward) until we bring down this military coup," he added.
Nationwide protests erupted yesterday after the crackdown by security forces on supporters of 62-year-old Morsi in Cairo and elsewhere killed hundreds of people. The protesters were demanding reinstatement of Morsi, Egypt's first democratically elected president, who was deposed by the army on July 3.
Egypt's army-backed interim Prime Minister defended the deadly operation by security forces against supporters of Morsi camped at Rabaa al-Adaweya and al-Nahda.