A mortar attack shattered windows in a residential area in the center of this city early Thursday.
Japanese troops are stationed in the southern Iraqi city for reconstruction work. Witnesses said there were no casualties.
Local public security authorities said two mortar shells caused the blasts. The explosions were the first serious attack in the city since the arrival of Ground Self-Defense Force troops last month.
One shell is believed to have been fired from near a soccer stadium about 2 km north of the downtown area. Another shell struck farming land several hundred meters east of the downtown area.
But at a Dutch military camp located a few kilometers south of where the blast took place, a GSDF official said, "We did not hear anything like an explosion."
In Tokyo, GSDF Chief of Staff Gen. Hajime Massaki told reporters that the GSDF is trying to confirm what happened.
The GSDF has been obtaining security information mainly from the Dutch forces and local police but will make its own efforts to find out what happened if necessary, Massaki said.
A witness said the first blast left a 20-cm-diameter hole in the ground, and that a cylindrical metal object was protruding from it.
In Samawah, Muthana Gov. Mohammed Ali Hassan called an emergency meeting on public safety in response to the mortar attack, a close aide said.
A local official said the attack might have been intended to frighten people and make them feel the security situation in the area is unstable.
Japan will deploy a total 550 ground troops to Samawah to provide water and medical aid and help repair public facilities there and in nearby areas.