Hundreds of Egyptians were trickling into Tahrir Square on Saturday morning to mark the third anniversary of the Arab Spring revolt that has violently split the country, the day after a string of bombings and clashes killed at least 18 people.
Saturday's festivities unfolded amid tight security under the threat of street-level riots and fresh terror attacks. Helicopters circled overhead as security personnel frisked revelers filing into the iconic protest center in downtown Cairo where a sound stage had been erected Friday evening.
Celebrations were already marred by a small explosion in front of a police training center early on Saturday morning in the dense Cairo neighborhood of Ain Shams, according to Egyptian state media. No casualties were reported from the attack.
Security forces are preparing for more violence on Saturday. The anniversary comes one day after six people were killed in bomb attacks across Cairo, one of them a rare truck bombing of the heavily defended headquarters of the security services, authorities said. An Al Qaeda-inspired group based in the Sinai Peninsula claimed responsibility for the suicide attack.
Twelve people, mostly civilians, were also killed in clashes throughout the country between police and supporters of Mohammed Morsi, Egypt's first freely elected president, who was ousted in a military coup last year.
The bombings come amid a campaign of insurgent attacks that began with Mr. Morsi's removal in July. They also come a day before the anniversary of the start of the popular revolt that toppled Hosni Mubarak, who ruled Egypt for nearly 30 years.
Egyptians were girding for more violence on Saturday, when millions of people are expected to gather throughout the country, many to celebrate the revolution, others to mourn it.