Riot police are lining up all the way from the protest tents in Rabieh up to the hill leading to the embassy. They're all holding batons and shields, and carrying in small boxes what I suspect to be teargas. There's a tank at every exit and some roads leading up to the embassy are closed.
This is probably why.
UPDATE: After two hours of being allowed to protest, clashes between the protesters and the police started taking place. The protesters threw rocks at the police and tried to advance toward the embassy, so the police dispersed the crowds with teargas and water cannons. For updated info check 7iber's watwet channel.