BAGHDAD — Rebuking their prime minister, Iraqi protesters demanding jobs and official accountability defied security forces Friday to throng central Baghdad and other cities, confronting the government with perhaps its biggest challenge since the chaotic aftermath of the American invasion that toppled Saddam Hussein 16 years ago.

At least 30 people were reported killed around the country, including eight in Baghdad, according to the Iraqi High Commission on Human Rights. It said at least 2,312 people were injured, mostly protesters, in angry confrontations with security forces.

In one Baghdad confrontation, masked officers shot volleys of tear gas canisters from a bridge to the Green Zone, the seat of Parliament and the prime minister, to drive back a crowd of unarmed demonstrators in Tahrir Square. Undeterred, the protesters surged again toward the bridge and were repeatedly repulsed.

The protests were a resumption of antigovernment demonstrations that started in the first week of October, but paused two weeks ago, after shootings by the security forces killed nearly 150 protesters nationwide, shocking the country and deepening disappointment with the government.