The Iraqi High Commission for Human Rights said 12 people died and 782 people had been injured since demonstrations started on Tuesday across the country to demand an end to corruption, better public services and jobs.
Iraqis have taken to the streets several times in recent months to protest against the government of Prime Minister Adil Abdul Mahdi, who took office last October.
Abdul Mahdi also the commander-in-chief of Iraqi forces said that all vehicles and individuals were totally forbidden to move in Baghdad as of 5 a.m. (local time) on Thursday, and until further notice, the state-run Iraqiya channel reported.
It said that the Abdul Mahdi's decision excluded travellers to and from Baghdad airport, ambulances and public services workers and vehicles.
The channel reported that it was up to provincial governors to decide whether to declare curfews in their provinces.
A police source told Efe news that protesters gathered at al-Tayaran Square in central Baghdad on Thursday, while another protest took place at al-Khulani square.
Security forces used teargas to disperse crowds, according to the official.
The US-led international coalition against the Islamic State terror organization said the rallies were continuing, urging all sides to reduce tensions.
"The loss of life and injuries - among civil and Iraqi Security Forces - is deeply concerning," a spokesman for the coalition Myles Caggins said on Twitter.
"We believe peaceful, public rallies are a fundamental element of all democracies; there is no place for violence," he added.
On Wednesday, four protesters and a police officer were killed and 50 others were wounded in al-Nasiriyah the capital of Dhi Qar province where the curfew was declared on Wednesday night until further notice.
Protesters stormed the regional government headquarters in al-Nasiriyah on the second day of unrest and set it ablaze, according to state television al-Iraqiya.
Meanwhile, the Internet service has been cut in all Iraqi provinces, except the semi-autonomous region of Kurdistan, since Wednesday.
Separately, an Interior Ministry source was cited as saying by Xinhua news agency that two mortar rounds landed after midnight on the Green Zone, which houses the main government offices and some foreign embassies in Baghdad.
There was no casualty reported by the mortar attack, the source said.
( With inputs from IANS )