It appeared to have been sparked when the Baghdad-based dailies published stories saying that a Shiite group lead by cleric Mahmoud al-Sarkhi was trying to dominate the holy city of Karbala.
The city, 90 kilometres south of Baghdad, is home to two revered Shiite shrines. In the last decade it has witnessed power struggles between Shiite militias.
Al-Sarkhi's group was not available for comment.
A group of men initially entered the office of the small Al-Parliman newspaper, demanding to meet the editor, the paper said in a statement posted on its website.
The men identified themselves as loyalists of al-Sarkhi and demanded to know why they published a report saying their leader was trying to take over communal Friday prayers at one of the holy shrines of Karbala.
The editor tried to mollify them, saying he believed the report was even-handed, the statement said.
It didn't satisfy the men.
As they left the editor's office, they appeared to signal to another group of men waiting outside. They smashed through the building's front door, shattering windows as they went through the building, Al-Parliman said.
They attacked reporters with batons, shoved computers onto the floor and tried to smash furniture, said the statement. They dragged one reporter to the building's roof and hurled him off, breaking both his legs, it said.
Editors al-Sheikh and al-Daraji offered similar accounts, except, they noted, the assailants also attacked them with knives.
Television footage following the attack on the Al-Mustaqila office showed computers strewn on the floor, the windows smashed. "The newspaper of lies, baseless claims and lies," was scrawled on a wall.
"It was so horrifying that we could not do anything," al-Daraji told The Associated Press.
A health official said five newspaper staffers were hospitalized, four with stab wounds. Al-Parliman said the fifth person was their staffer, pushed from the building's roof.
The health official spoke anonymously because he wasn't authorized to speak to the media.
Al-Sheikh said he also recognized the attackers as militant Shiites belonging to al-Sarkhi's group. Al-Daraji said they had run a similar story, but also published a response from the Shiite cleric's office.
It was not immediately possible to obtain comment from the fourth newspaper attacked, Al-Nas.
The four newspapers are considered modestly sized. The largest, al-Dustour, claims a run of 12,000 copies daily.
In response to the attacks Tuesday, blue-khaki clad police set up checkpoints through the middle-class Karradeh neighbourhood, snarling traffic.
Iraq is ranked among the most dangerous places in the world for journalists, according to the New York-based Committee to Protect Journalists. At least 150 reporters and 54 support workers were killed in Iraq from the start of the U.S.-led invasion in March 2003 to the pullout of foreign troops in December 2011.
They did not have immediately updated figures for 2012.
Such attacks have been less common of late. The last major attack on reporters was the slaying of a television presenter Ghazwan Anas in July 2012, who worked for a channel in the predominantly Sunni northern city of Mosul.
The New York-based group said in a March statement that Iraq has never charged a person for killing a reporter. The "impunity rate . is the worst in the world. It is 100 percent," the statement said. "Even today, as Iraq has moved beyond conflict, authorities have shown no interest in investigating these murders."
Iraqi government spokesman Ali al-Moussawi condemned the attack. "Security forces have taken action and some of the (assailants) have been arrested and we are interrogating them," he said.
Al-Parliman said in its statement that it couldn't issue news Tuesday, because the assailants had smashed all its equipment.
In other violence, a provincial official said gunmen attacked workers at a remote gas field near the Syria border, killing two men and kidnapping one.
Farhan Farhan, the mayor of the western town of al-Qaim, said the gunmen set fire to workers' trailers at a camp near the gas field, killing an engineer and a manual laborer. The kidnapped man is the brother of the head of the Iraqi company building the camp site.
Farhan said the attack took place on Monday. He says the Iraqi company was contracted by South Korea's KOGAS to build the trailer camp before developing the gas field. No KOGAS employees were on site.
Al-Qaim is about 320 kilometres west of Baghdad, just across the border from Syria. Iraqi militants are believed to be taking advantage of Syria's turmoil and the porous border to rebuild their strength in this region.
