Ground Self-Defense Force troops deployed to the southern Iraqi city of Samawah have found themselves threatened by mortar and rocket attacks for three straight nights, prompting concerns about the security situation.

Defense Agency officials said personnel in the GSDF camp heard one explosion at around 3 a.m. Tuesday. The noise seemed to come from a few kilometers to the north, the officials added.

No Japanese troops were wounded, the agency said, adding they were trying to confirm the type of ordinance as well as the exact point of impact.

"We cannot deny the possibility that the SDF is the target of these attacks, although we do not as yet have solid information to confirm this," Defense Agency chief Shigeru Ishiba told a regularly scheduled news conference Tuesday morning.

Yet Ishiba maintained that Samawah is still a "noncombat zone."

A special law allowing GSDF troops to be dispatched to Iraq states they can only operate in noncombat zones -- a controversial notion created out of consideration for the pacifist Constitution, which prohibits Japan from using force as a means of settling international disputes.

The security situation in Samawah appears to have been deteriorating over the past few weeks as fierce fighting continues between U.S.-led forces and Shiite militants led by radical cleric Muqtada al-Sadr in the holy city of Najaf in neighboring Najaf Province.