Once at the forefront of the fight against global warming, Japan is now facing calls from other big economies such as China to set fresh emissions targets as Tokyo increases its use of dirty coal energy to replace nuclear.

Japan is the world's fifth-biggest emitter of carbon dioxide but has watered down emissions targets due to the shutdown of its nuclear plants in the wake of the 2011 Fukushima disaster, with utilities burning a record amount of coal for power generation.

China and the United States, the world's biggest economies and polluters, as well as the European Union, have committed to new targets in the last few months. Japan now finds itself alongside India and Russia, the world's third- and fourth-biggest polluters, by not yet declaring goals.

Officials at Japan's industry and environment ministries denied any backsliding on climate policies and said a joint committee was discussing new goals to cut emissions, and aimed to come up with proposals as soon as possible.

But analysts say Japan's room for maneuver is limited after Tokyo eased rules for coal plants amid plans to raise coal-fired capacity by nearly 40 percent.

"We expect Japan would certainly come up with an ambitious target for the post-2020 period. That is not just China's expectation I think it is the expectation of the world," said China's delegation leader Su Wei at climate talks taking place until Friday in Lima ahead of a 2015 U.N. summit in Paris.

Japanese delegates in Lima also said the government aimed to have targets as quickly as possible but gave no timeline.

China, the European Union and environmentalists criticized Japan last year after it threw out a plan to cut emissions by 25 percent from 1990 levels and diplomatic sources say they are alarmed about its shift toward coal.

Japan was a leading proponent behind the 1997 Kyoto Protocol which committed countries to binding emissions reduction targets and pushed for it to be named after its former imperial capital.

"Japan cannot excuse itself in Paris COP21 by saying 'sorry we don't have nuclear power so we can't reduce CO2 emissions,' " said Nobuo Tanaka, an adviser at the government-affiliated Institute of Energy Economics.

Prime Minister Shinzo Abe wants to restart reactors but is facing strong public opposition from voters wary of nuclear power after Fukushima.

The Paris U.N. summit in 2015 aims to finalize an agreement as part of long-term efforts to limit average temperature rises to 2 degrees above pre-industrial times.

Countries are meant to announce plans for emissions reductions after 2020 by an informal deadline of March 31, 2015.

In November, China and the United States pledged to set new limits on carbon emissions from 2025.

Carbon emissions in Japan rose 1.6 percent in the year through March to a record.

Encouraged by eased environmental rules, companies are planning to install about 14.8 gigawatt of coal-fired capacity, an increase of 37 percent, in coming years.

Japan's appetite for cheap coal, to counter a soaring oil and gas bill after the nuclear shutdown, saw it import a record 109 million tons of coal in 2013.