At least 51 people were killed and 435 injured in clashes early Monday near the Republican Guard headquarters in the Egyptian capital, the Ministry of Health said.
Supporters of deposed President Mohammed Morsi had been holding a sit-in near the compound.
Reuters cited the Egyptian military as saying "a terrorist group" had tried to storm the building early Monday. A Ministry of Defense official said that 200 people were arrested after protesters attacked the site around 4 a.m. local time (10 p.m. ET on Sunday). Some were armed with guns, Molotov cocktails and knives, according to the official. One officer was killed and six troops wounded, the military said.