Environment Minister Tetsuo Saito believes a plan to slash greenhouse gas emissions by 7 percent by 2020 from 1990 levels is "not ambitious enough" and the nation should be able to achieve a 15 percent cut.

A 7 percent cut was supported by 45.4 percent of respondents in a government opinion poll released in late May.

Saito said however political will and appropriate policies would enable Tokyo to realize a 15 percent cut in carbon dioxide and other heat-trapping gases.

A government study panel has presented six options for the greenhouse gas emissions target for 2020, ranging from a 4 percent increase to a 25 percent cut from 1990 levels. The government is set to determine its 2020 reduction goal in mid-June.

A 2020 target is seen as crucial for Japan and other countries because it is the major focus of U.N. negotiations for a successor treaty to the carbon-capping Kyoto Protocol, which expires in 2012. The talks are scheduled to conclude at a key U.N. climate change conference in Copenhagen in December.

For Japan to lead negotiations on setting a new emission cut framework, it is necessary for the country to demonstrate its commitment to contributing to the fight against global warming, Saito said.

The minister said if the government is to decide a 2020 target with a range, the maximum figure for emission cuts should be "ambitious."

Saito reiterated his position that Tokyo should aim for a 25 percent reduction in total — 15 percentage points by domestic efforts and the remaining 10 points by forest absorption and the purchase of emission credits from other countries.