Under plans announced in June, the deployment of mainly non-combatants on a relief and rehabilitation mission was to take place in stages over several weeks beginning in early August.
The government warned it would consider legal action - using a law to protect military secrets - against any media outlet that violated the ban.
"This is a secret military operation. We don't want to give terrorists any information on our troop movements," a Defence Ministry official said, adding that reports ignoring the blackout would be viewed as a serious breach of security.
Defence Minister Yoon Kwang-Ung said "appropriate measures" would be taken against offending media outlets.
Third largest group
The South Korean contingent, the third largest in the US-led occupation force in Iraq, is scheduled to take up positions in Arbil, a Kurdish-controlled town in the north.
Protesters also rallied near the
US embassy in Seoul last month
Several hundred activists staged protests against the troop dispatch on Tuesday at a training camp south of Seoul.
Foreign Minister Ban Ki-Moon, in a joint press conference with Defence Minister Yoon on Wednesday, said security of South Korean troops and civilians was paramount.
"In relation to the dispatch of troops, the government is doing its best to secure the safety of its citizens as well as soldiers," he said.
More than 30 nations have sent troops to Iraq to join the US-led force, but Seoul stands alone in imposing a tight media blackout.
South Korea's parliament approved the dispatch in February, but stipulated that troops would engage in relief and reconstruction work only and would avoid combat.
The body of translator Kim Sun-Il was found near Baghdad in late June after South Korean President Roh Moo-Hyun rejected demands from his captors to cancel the troop deployment.