Japan will not ratify the 1997 Kyoto Protocol to curb global warming if the United States stays out of it, Foreign Minister Makiko Tanaka said Friday.

"Japan cannot go ahead with European countries while leaving behind the U.S. We will make constructive efforts to the end to ratify the pact jointly with the U.S.," Tanaka said at the House of Representatives Foreign Affairs Committee.

The Kyoto treaty imposes binding limits on emissions of six greenhouse gases, including carbon dioxide. The U.S. is the world's largest emitter of carbon dioxide.