The Diet is set to enact an antipiracy bill Friday to establish a permanent law that will enable the Maritime Self-Defense Force to protect vessels of any nationality off Somalia, by use of force if necessary.

An Upper House defense committee controlled by the opposition rejected the bill Thursday, as the Democratic Party of Japan argued that Diet approval should be required for the government to deploy MSDF units overseas to hunt pirates.

But the bill is nevertheless expected to clear the Diet Friday, when the Lower House puts it to a second vote.

"We believe piracy off Somalia is a life-or-death issue that threatens Japan's interests, which are to secure the safety of marine transport," Prime Minister Taro Aso said during the Upper House session.

Social Democratic Party lawmaker Tokushin Yamauchi argued that easing the use of arms would violate the Constitution, which he said bans the MSDF from using force abroad.

The use of force "is an act that would attack the core of the Constitution, which prohibits the use of force abroad and the dispatch of the military in the name of national interests," Yamauchi said.

But Aso argued that since piracy is a crime, using weapons to combat it is a police activity and does not therefore violate the Constitution.

"Piracy is a criminal act by a private individual for his or her personal gain," Aso said. "Therefore, the use of weapons is within the legal framework of Japan's criminal code . . . and that is completely different from the use of military power prohibited by the Constitution."