Tokyo Electric Power Co spent $358 million in the past two years on carbon credits, Japan's biggest utility said on Thursday, as it tried to achieve a self-imposed target to help Japan to fight global warming.

TEPCO, one of the world's most active buyers of carbon credits, did not say how much delivery it received in CO2 equivalent in the two years to March 2009, or the volume of carbon credits it bought from abroad for the 34.9 billion yen ($358 million).

All power firms in Japan have said that if their efforts to make low-carbon electricity are insufficient they will buy carbon offsets from abroad as allowed under the Kyoto Protocol.

As an industry, each power firm is set to emit 20 percent less CO2 per kilowatt hour than the 1990 levels over the five-year period of the Kyoto agreement to March 2013.

TEPCO in particular is struggling to sufficiently reduce the amount of carbon required to produce a single unit of electricity as a 2007 earthquake forced it to shut the world's biggest nuclear plant, forcing thermal plants to run harder.

TEPCO has said it emitted an estimated 0.42 kg of CO2 per kilowatt hour in 2008/2009, little changed from 0.425 kg in the previous business year and far short of its Kyoto target of 0.30 kg.

Japan's power industry as a whole has so far procured 190 million metric tons in CO2 equivalent, mainly by early investment in clean energy projects in developing countries. At current prices of 11 euros ($14) a metric ton, that is about $2.7 billion.

In its annual earnings report, TEPCO allocated the cost to general administration related to its power business.

TEPCO declined to give further details on carbon credits such as types of credits or how much CO2 equivalent it has purchased so far for delivery during the Kyoto period.

Disclosing our costs of carbon credits per (metric) ton would have some impact on the carbon market, a company spokesman said.

($1=97.50 Yen; $1=.7508 Euro)

(Reporting by Risa Maeda; Editing by Michael Watson)