Japanese officials vowed Thursday not to back out of reconstruction efforts in Iraq after a series of explosions were heard outside a Japanese camp in the Mideast nation.

Japan's (search) Defense Agency was investigating three explosions, reportedly set off by a mortar or rocket, heard overnight near the troops' base camp in Samawah (search). No injuries or damage were reported.

"Terrorists just want to create confusion. They are trying to make the Self-Defense Forces withdraw," Prime Minister Junichiro Koizumi (searchtold reporters. "I think this was part of such scare tactics."

The explosions were aimed at the troops and were a threat the government takes seriously, but it would not make Japan withdraw from its humanitarian mission, the government's top spokesman said.

"We don't know why they targeted the Self-Defense Forces," Chief Cabinet Secretary Yasuo Fukuda said. "We will continue to do what we can while investigating."

Japan has about 530 ground troops based in Samawah, part of a total deployment of 1,100 soldiers for a mission in Iraq to purify water and carry out other reconstruction tasks.

Concerns have been growing in Japan that the recent upsurge in violence in Iraq could affect the troops, who are strictly non-combat.

Roads were reportedly blocked off to vehicles following the incident by local authorities. Dutch troops were also helping to investigate the area amid reports that a shot may have been fired near their base as well.

A hole believed to have been caused by a mortar round was later found in the ground outside the base, Vice Defense Minister Takemasa Moriya said.

Earlier this week, Japanese soldiers postponed repair work they had been conducting on roads and schools outside base grounds to avoid trouble.

The Japanese contingent will continue to supply drinking water to local communities, Moriya said.

"The troops there have been playing close attention to safety. They have been trained and they have been prepared," Koizumi said.

Japanese public opinion is split over the mission. The government says the deployment is needed to help rebuild Iraq, but critics fear the troops could be drawn into the fighting.