Defence chief Yoshinori Ohno paid a brief visit on Sunday to Japanese troops in Iraq and said they were in a "stable" area and being welcomed by Iraqis, days before an expected announcement on the deployment's extension.
Japan's main opposition leader Katsuya Okada, who wants the troops pulled out when the mission expires on 14 December, called Ohno's trip "nothing but a simple show".
"Some people criticise anything," Koizumi said on Monday, adding that he trusted Ohno's opinion.
"I will listen to his report," the premier said. "I will look carefully at the situation and then decide."
The nearly 600 troops' initial one-year mission deadline expires on 14 December but local media reports said the government was set to announce an extension on Friday.
The dispatch is Japan's first to a country of active combat since the second world war. About 61% of Japanese want troops to leave Iraq amid concerns about security, a Nihon Keizai newspaper poll said last month.
Japanese troops are stationed
in the Iraqi Shia city of Samawa
Ohno on Sunday spent several hours in Samawa, the Shia Muslim town 250km south of Baghdad where Japan's Self-Defence Forces troops are based.
Ohno was the first senior Japanese official to visit Iraq since the US-led war, which was strongly backed by Koizumi.
"I visited the city of Samawa and nearby roads and reconstruction sites," the defence chief said in a statement. "The local security is stable and I confirmed that the Self-Defence Forces' activities are welcomed by the Samawa people.
"The demands for road and school repairs and medical assistance are still numerous and I reconfirmed the continued need for SDF humanitarian assistance," he said.