Japan is planning to pledge a 26 percent cut in its greenhouse gas emissions from 2013 levels, ahead of a global summit on climate change this year, officials said Friday.

The figure, using 2013 as the base year, was proposed at a government panel this week and will go out for at least a month's public consultation before being set in stone by the cabinet, an environment ministry official told AFP.

Prime Minister Shinzo Abe will likely formally announce the target at the Group of Seven (G-7) summit in Germany in late June, local reports said.

The pledge was immediately dubbed unambitious by environmental groups, with Tokyo-based campaigners Kiko Network pointing out that 26 percent cut from 2013 works out at just 17 percent cut from 1990 levels.

The numbers come after Tokyo proposed this week a fifth of its electricity should come from nuclear power generation, despite widespread opposition in the aftermath of the Fukushima disaster.

Japan's intended energy mix -- what proportion of power comes from which sources -- has been a subject of hot debate for months, not least because without it, Tokyo has been unable to make international commitments to reduce greenhouse gas emissions.

With none of the nation's viable nuclear reactors in operation, the target indicates an intention to bring most, if not all of them, back online.

Japan is one of the few leading polluters that has not yet declared a target on emission cuts, as the world works towards a new framework for combating climate change, to be finalised at December's COP 21 gathering in Paris.

A total of 33 polities -- including the number two emitter the United States, the number three emitter the European Union, and Russia, ranked fifth -- submitted their reduction goals to the UN secretariat by the end of March.

In order to achieve the proposed emissions cut, Japan will also ramp up its reliance on renewables such as solar and wind power, which, under the energy mix proposal would account for 22-24 percent of Japan's whole electricity demand in 2030, double the current portion.