Former U.S. prisoners of war forced into slave labor for private Japanese companies during World War II are accelerating their campaign to seek compensation from the companies that profited from their work.

But Japan has rejected the demand, saying the issue was settled under an international treaty ratified by the United States 50 years ago. Tokyo says it is ready to fight any legal action mounted by the POWs.

Moves to seek reparations from Japanese companies over wartime forced labor stem from last July's passage of a California statute allowing former POWs held by Nazi Germany, Japan and their allies to file World War II damages suits until 2010.

Based on that law, some 30 lawsuits have already been filed in California courts by former POWs against Japanese companies.