A district court ruling Wednesday that a visit to Yasukuni Shrine by Prime Minister Junichiro Koizumi was unconstitutional has ignited debate on the need for an independent court that specializes in constitutionality.

The topic has been a focus of Diet debate on constitutional reform, which went into full swing in 2000 following the establishment of the Constitutional Research Committee in both houses of the Diet.

The Constitution stipulates that the Supreme Court is "the court of last resort" and has the power to determine the constitutionality of any law, order, regulation or official act.

But constitutional judgments by the top court are rare, partly because it is busy dealing with a flood of appeal cases and partly due to its restraint in passing judgment on sensitive political matters, lawmakers said.

"The ruling brings up a number of questions," Yoshito Sengoku, a lawmaker of the Democratic Party of Japan, told the Lower House constitutional committee on Thursday.

He said there is a contradiction in that the district court is powerless to stop Koizumi from visiting the shrine while issuing a "grave decision" that his act violates the Constitution.

He said, "Japan needs to set up a constitutional court to make a responsible judgment."

Many lawmakers have voiced caution against the establishment of a new court specializing in judging constitutionality.

Tomio Yamaguchi, a Japanese Communist Party lawmaker, said Koizumi must stop visiting the shrine.

"Even if it is a district ruling, the result must be respected," he said.

Yamaguchi said it should be easier for the Supreme Court to rule on constitutionality.

But Yoji Nagaoka, a Liberal Democratic Party lawmaker, reckoned courts should refrain from ruling on political matters and obey the separation of legislative, administrative and judicial powers.