CAIRO—Egyptian government officials said police could crack down as early as Monday on two vast camps in Cairo supporting ousted President Mohammed Morsi, a move that could lead to clashes as impassioned demonstrators hunker down in the tent cities.

Thousands of protesters have created a vast city of their own within Cairo's Raba'a al Adiwiya square over the past six weeks, pitching tents that now house pharmacies, bouncy castle playgrounds and entire families. As children slept on a recent night, sounds of wedding celebrations and political chants filled the evening air.

But the camp's labyrinth of alleyways brimming with antigovernment demonstrators poses a logistical challenge to the Egyptian authorities, known for their use of force in clearing past protests. The military-installed Egyptian government announced last week that it would clear out Raba'a and Nahda square, home to the smaller camp, after negotiations over the current political stalemate with the Muslim Brotherhood failed.

The police say they plan to lay siege to the tent cities, using tactics such as creating cordons and refusing to allow food and water to enter the sit-ins. Muslim Brotherhood officials and camp residents say they are determined to withstand any blockade. To thwart the crackdown, protesters have used jackhammers to break up roads and erected a large, covered wooden structure at one of Raba'a's main entrances. Volunteers sporting hard hats and sticks guard the fortresslike walls.

"Do you know the Prophet Muhammad?" asked Essam El Erian, a senior Brotherhood official. "He and his followers lived for three years under siege by the infidels without food or water."