BEIRUT—Iranian authorities deployed in force across Tehran Wednesday to conduct last-minute security sweeps and warn residents to refrain from joining antigovernment protests planned for Thursday.

The government typically orchestrates large, carnival-like rallies and demonstrations to mark the anniversary of the Islamic Republic. For this year's events on Feb. 11, the day marking the culmination of the annual celebrations, opposition leaders have called for protesters to demonstrate against the regime. That has set the stage...