CAIRO — Thousands of supporters and opponents of Egypt’s embattled Islamist president held rival sit-ins in separate parts of Cairo on Saturday on the eve of opposition-led mass protests aimed at forcing Mohammed Morsi from power.

The demonstrations follow days of deadly clashes in a string of cities across the country that have left at least seven people dead, including an American, and hundreds injured. The violence — and wide expectation of more to come Sunday during rallies that the opposition says will bring millions into the streets — has fed an impending sense of doom in the country.

Egypt has been roiled by political unrest in the two years since uprising that ousted autocrat Hosni Mubarak, but the upcoming round of protests starting Sunday promises to be the largest and perhaps the bloodiest. The turmoil has compounded the country’s social and economic woes, with crime surging, unemployment high and with shortages of basic items not uncommon.