Baghdad (CNN) -- The angry mobs barged into the newspaper buildings, in the heart of bustling Baghdad. They smashed equipment, stole files, beat up guards and workers, and tossed one person from a roof.
The assaults, which unfolded simultaneously Monday, apparently stemmed from outrage over a story seen as critical toward a Shiite cleric in Karbala. Police investigated the incidents on Tuesday.
The U.N. mission in Iraq slammed the assaults as "unacceptable under any circumstances." UNESCO in Iraq stressed concern over the impact of the attacks.
"Freedom of expression is a crucial element for establishing true democracy and building sustainable peace in Iraq," UNESCO Director in Iraq Louise Haxthausen said.
Before the attacks, Younis al-Arraf, editor of the Parliament, said he met with angry followers of Mahmud al-Sarkhi, a firebrand Shiite cleric, according to the Journalistic Freedom Observatory (JFO), an Iraqi media watchdog.
They discussed a piece in the Parliament suggesting the cleric is planning to take over the Shiite religious authority in Karbala by force.
The article also said the al-Sarkhi's residence in Karbala, in the Shiite heartland of southern Iraq, resembles an armed camp, with the location protected by dozens of followers armed with sticks and knives.
Al-Arraf said he explained to the people incensed with the article that it was written by a news agency, not produced by the paper itself.
But later, attackers entered the buildings of four independent dailies in Iraq's capital -- the Constitution, the Iraqi Future, the People and the Parliament, the observatory said.
At least six people were injured, police said.
Employees of a fifth Baghdad daily newspaper, al-Mada, received threats on Tuesday, the paper's director general told CNN. Mada means "range" in Arabic.
A spokesman for the cleric said his office had nothing to do with the attacks and condemned them. The JFO condemned the attacks and called on authorities to investigate and protect journalists.
After the fall of Iraqi leader Saddam Hussein and and the advent of democracy, a vibrant media scene has emerged in Iraq, with a slew of newspaper and broadcasting outlets independent or affiliated with political movements.
But journalism can be a perilous calling in Iraq, one of the most dangerous countries for journalists to practice in since 2003, when the war there began.
CNN's Mohammed Tawfeeq reported on this story from Baghdad; CNN's Joe Sterling reported from Atlanta.