Defence Minister Shigeru Ishiba had planned to visit Iraq to boost the morale of the roughly 550 troops in the southern city of Samawa, where they are on a reconstruction mission, the Kyodo news agency said on Tuesday, quoting government sources.
A defence ministry spokesman declined to comment on the report, which said the plan was scrapped because of a Shia revolt in southern Iraq and the kidnapping of foreign nationals, including three Japanese civilians whose fate is still unknown.
An incident involving Ishiba could affect public support for the ruling coalition, which faces a parliamentary election in July.
Japan, sharply divided over the troop dispatch from the outset, has been on tenterhooks since kidnappers released a video last Thursday showing the three blindfolded and with guns to their heads.
Prime Minister Junichiro Koizumi said there was no definite information on the fate of the hostages.
"I still cannot say anything definite. There are many points that are unclear," Koizumi told reporters.
The hostages' relatives have swung between joy and despair since Thursday, as reports suggesting that the hostages would soon be released failed to be realised.
The three hostages are Naoki Imai, 18, who wanted to investigate the effects of depleted uranium weapons, freelance journalist Soichiro Koriyama, 32, and aid worker Nahoko Takato, 34.
"Koizumi! You dragged us into this war. You get us out now!"
Koizumi's handling of the crisis could affect his public support and that of the ruling coalition, which faces a parliamentary election in July.
A weekend opinion poll by TV Asahi indicated only 38% of respondents felt the government was taking enough steps to secure the hostages' release.
On Tuesday, about 800 people gathered before the prime minister's official residence to protest against the dispatch of the troops and Koizumi's handling of the hostage crisis.
Ruling Liberal Democratic Party lawmaker Koichi Kato, one of the party's few outspoken critics of the dispatch, said Japan should rethink its decision.