Egyptian Muslim Brotherhood members gathered outside their Cairo headquarters on Friday in anticipation of an opposition march on the building where activists previously clashed with the Islamists.
The Brotherhood bussed in hundreds of supporters to stand guard outside its offices ahead of the opposition protest, set to begin after noon on Friday.
A senior Brotherhood member said on Thursday the Islamists would defend their headquarters if police failed to protect it.
The Brotherhood has seen about 30 of its offices across the country attacked in widespread protests against President Mohamed Morsi, the Islamists' successful candidate in last June's election.
Activists, including often violent Black Bloc protesters, have called for a demonstration outside the Brotherhood headquarters on Friday, almost a week after they clashed with the Islamists and police guarding the building.
The Brotherhood, well-organised despite decades of persecution by now overthrown president Hosni Mubarak and his predecessors, was the main winner of parliamentary and senate elections last year.
But its critics accuse it and Morsi of mirroring the tactics used by Mubarak, who was overthrown in 2011, against the opposition.