WATCH: Iraq death toll after Nasiriyah massacre continues to rise
Security forces were sent to two bridges in the southern city which have been held by protesters for several days and ordered troops to quell the uprising.
Live fire and tear gas were fired at activists in the area killing demonstrators, according to The New Arab's Arabic-language sister publication.
Two protesters were also shot dead in Iraq's Najaf, medical sources said, in a crackdown near the burnt Iranian consulate in the Shia shrine city, bringing the total death toll on Thursday to 27.
Iraqi Prime Minister Adel Abdel Mahdi, as commander in chief of the armed forces, ordered military chiefs to "restore order" in southern cities hit by uprisings.
Iraqi sources told The New Arab's sister-site that security forces had carried out wide scale arrests of activists in Najaf, while 15 protesters were reported injured.
The holy Shia city was hit by demonstrations on Wednesday night that led to the Iranian consulate being torched by protesters, enraging Tehran.
Iran's foreign ministry meanwhile "communicated its disgust to the Iraq ambassador in Tehran" at the incident.
Iran's key overseas commander, General Qasem Soleimani, Tehran's point man on Iraq, has met with security officials in Baghdad and Najaf and urged the government to crackdown on the protests, which have demanded Tehran end its interference in Iraqi politics.
Sources told The New Arab's sister site that the 9th and 6th Iraqi Army divisions arrived in the Iraqi city of Najaf and Karbala to deal with the anti-government uprisings, which have mostly been concentrated in the capital Baghdad and Shia south.
Iran-linked Popular Mobilisation Forces militias have also reportedly issued threats to the protesters, according to sources.
Amnesty International said Nasiriyah ressembled a "warzone" after the crackdown by security forces.
"This brutal onslaught is just the latest in a long series of deadly events where Iraqi security forces meted out appalling violence against largely peaceful protesters," said Lynn Maalouf, Middle East Research Director at Amnesty International.
The death toll from Iraq has risen to 360 with over 15,000 wounded according to an AFP tally, with the vast majority of casualties reported to be protesters.
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