Media playback not supported on the device
In Iraq's capital, Baghdad, curfew is applied two days after the clashes between anti-government protesters and security forces.
Restrictions remain in effect until further notice. Curfew has already been declared in three other cities in protests against job shortages, poor services and corruption.
At least seven people died and hundreds were injured in the violence.
In some regions, social media platforms and internet access have been blocked.
Since Adel Abdul-Madi's inauguration a year ago, the biggest demonstration has been the lack of organized leadership.
The government has vowed to settle the protesters' concerns by criticizing the insecure rioters.
What are the curfew terms?
Prime Minister Abdul Mahdi said in a statement that Thursday at 5 am (02:00 GMT) in Baghdad, "all vehicles and individuals cannot move completely."
Travelers to and from the city's airports, ambulances, hospitals, government officials in the electricity and water departments, and religious pilgrims were exempt from curfew.
The southern cities Nasiriya, Amara, Hilla already had limitations.
Media playback not supported on the device
The United Nations urged the authorities to exercise arrest. "All individuals have the right to speak freely according to the law," said UNESCO spokeswoman Jeanne Hennis-Plasschaert.
More in Iraq:
What happened in Baghdad?
In the capital, police fired tear gas and fired ammunition to disperse protests in various areas.
The protesters also tried to reach central Tahrir Square, where police were sealed, with a nearby bridge leading to the Green Zone, where government buildings and foreign embassies were located.
After the US-led invasion of Iraq in 2003, the Green Zone, which was outside the boundaries of most Iraqis, resumed in public in June.
Facebook, Twitter, Whats app, Instagram and other social and messaging apps have been blocked by several Internet providers since Wednesday at 15:30 (12:30 GMT), according to the netblock site.
“We are asking for change. We want the downfall of the entire government. ”A protester in Baghdad told Reuters that he wanted to remain anonymous because of fear of retaliation.
The Ministry of Home Affairs says, "To mobs who aim to undermine the meaning of [protesters’] "Peace Needs and Elimination".
Image copyright
Reuters
Prime Minister Adele Abdul Mahdi expressed regret for violence
What did Mahdi PM say?
On Tuesday night, Prime Minister Abdul Mahdi expressed regret for the violence and promised an "investigative reason" investigation into the protest.
"This saddens me and makes me sick with injuries between demonstrators, our sons, security forces and the destruction and looting of public and private property," he wrote on Facebook.
"We emphasize that our priorities will continue to focus on providing fundamental and realistic solutions to many of the problems accumulated over decades."
The prime minister also said he would create more jobs for graduates. According to the World Bank, the youth unemployment rate in Iraq is currently around 25{7be40b84a6a43fc4fae13304fce9a2695859798abfc41afd127b9f8b21c5f9c5}.
Last year, the southern Iraqi city of Basra suffered weeks of protests against unsafe drinking water, power shortages, unemployment and corruption. Government officials, including the main local council building, got off.