An Interior Ministry source told Efe news that most of the curfew violations occurred in downtown Tahrir Square and adjacent streets, as well as areas in the capital's east, such as Palestine Street and Sadr City.
Sadr City has a Shia majority and is the stronghold of the renowned cleric Muqtada al-Sadr, who has backed the protests and encouraged this new wave of demonstrations that began October 25.
According to Efe news, hundreds of people marched on foot and in vehicles along 14th Ramadan Street until late at midnight - when restrictions on citizens' right of movement took effect - but later withdrew after repeated requests from the security forces.
Since October 25, at least 82 people have been killed and more than 3,000 injured in clashes between protesters and security forces.
The Baghdad Operations Command said in a statement that the decision to impose the curfew will remain in force "until further notice", adding that the measure aimed to protect demonstrators and prevent "infiltrators" from attacking them.
This new wave of protests follows the initial demonstrations that erupted on October 1, which spread through the capital and other regions of Iraq due to outrage over the lack of public services and employment opportunities.
At least 157 people died in the ensuing unrest, including eight members of the security forces.
( With inputs from IANS )