CPJ’s executive director, Ann Cooper, made the call for a public inquiry into the death of the award-winning journalist in a statement published on the internet.
Mazin Dana was killed by an American tank crew outside Abu Ghuraib prison in the western quarter of Baghdad on Sunday while he filmed the scene of an earlier mortar attack that killed six Iraqis.
"In the midst of frequent violence, and often under attack himself, Mazin was a determined witness who took constant risks in order to tell the world the news," Cooper said.
Earlier, US-led occupation forces said its troops had "engaged" a Reuters cameraman when soldiers thought his camera was a rocket-propelled grenade launcher.
Reuters Chief Executive, Tom Glocer, has also called for "the fullest and most comprehensive investigation into this terrible tragedy".
Dana is the second Reuters cameraman to be killed since the invasion and occupation of Iraq. His death brought to 17 the number of journalists or their assistants who have died in Iraq since the war began on 20 March.
The families of two Iranian journalists held by US occupation forces in Iraq gathered in front of the British embassy in Tehran on Monday, asking the British government to facilitate their immediate release.
The embassy's second secretary, Andrew Greenstock, told reporters after a meeting with four family members that "the embassy will continue to actively follow up this case with the coalition provisional authority in Baghdad".
Wahid Abu Talib, the brother of one of the journalists, told reporters "they told us that since it has become evident that these two (Said Abu Talib and Suhail Karimi) are journalists ... we hope to release them soon."
Said Abu Talib's wife said it has been 48 days since they were arrested by the US forces, but that she still had not received any official notification.
The two, plus an Iraqi interpreter and a driver, were working on a documentary in the mainly Shia region around Diwaniyah, in the south of Iraq, when they were arrested and taken to a US base in Diwaniyah.