Egyptian protesters chant against the Muslim Brotherhood and President Morsi outside the presidential palace in Cairo, Egypt, Dec. 6, 2012.(Photo: Hassan Ammar, AP)
CAIRO - The Muslim Brotherhood pledged to bring down Egypt's military-backed interim government Thursday, deepening the country's political crisis as the death toll from clashes between security forces and supporters of ousted President Mohammed Morsi climbed to 421.
"We will rise and rise again until we push the military back into the barracks and restore democracy," Gehad El-Haddad, spokesman for the Islamist organization, said on his Twitter feed.
"We will not bow down, we will not cower," said El-Haddad, adding that the security forces had shown "unbelievable brutality".
The Muslim Brotherhood also announced plans to hold a march Thursday in Cairo.
El-Haddad's call to arms followed a bloody day of unrest in Egypt, after security forces - backed by bulldozers - cleared two Cairo sit-in camps protesting the military's removal of the country's democratically elected leader. The health ministry announced early Thursday that the death toll from subsequent clashes reached 421, with 3,572 others injured.
The violent clearance of the camps triggered a backlash around Egypt, prompting the interim government to declare a month-long state of emergency and impose a night-time curfew.
It also led to international condemnation - Secretary of State John Kerry described the situation as "deplorable" - and the resignation of Nobel Peace Prize winner and interim government minister, Mohamed ElBaradei.
In a troubling indication of the increasingly sectarian nature of Egypt's divisions, security sources and state media reported that a number of churches had been attacked across Egypt, Reuters reported.
Churches were attacked in the Nile Valley towns of Minya, Sohag and Assiut, where Christians escaped across the roof into a neighboring building after a mob surrounded and hurled bricks at their place of worship, state news agency MENA said.
Authorities referred 84 people from the city of Suez, including Muslim Brotherhood members and supporters, to military prosecutors on Thursday on charges of murder and burning churches, the state news agency reported.
As Egypt awoke to the first full day of its month-long state of emergency, Cairo appeared calm and traffic flowed through the former site of the Rabaa camp, according to Reuters. The overnight curfew stemmed most of the violence, with usually-crowded streets deserted.
But while the streets were quiet, activists rallied online - using social media to collate pictures and first-hand accounts of Wednesday's violence at the Rabaa and Nahda camps.
Images of bodies piled high in mosques and other makeshift morgues were posted on Twitter, while on Facebook one activist set up a gruesome gallery showing victims of the violence.
Egypt's Interior Ministry also posted pictures - of the 13 policemen killed by pro-Morsi protesters who fought back during the camp clearances.
The turmoil is the latest chapter in a bitter standoff between Morsi's supporters and the interim leadership that seized control of the Arab world's most populous country on July 3.
Morsi's removal came after millions of Egyptians massed in the streets at the end of June to call for him to step down, accusing him of giving the Brotherhood undue influence and failing to implement vital reforms or bolster the ailing economy.
Morsi himself has been held at an undisclosed location, and faces charges - brought by the security forces - that he colluded with Palestinian militants.
By Ayman Mohyeldin and Alastair Jamieson, NBC News