Japan’s government has reportedly been challenged by US officials over its backing of overseas coal-fired power plant development.

According to an unnamed US government source “with direct knowledge of the matter” quoted by the Reuters news service, the US has told Japan that the coal-fired power projects it backs overseas need to include carbon capture and storage (CCS) as well as clean coal technology.

Reuters said the source “declined to be identified due to the sensitivity of the matter”.

Japan announced in August that it would increase its support for foreign clean coal plants through public loans and insurance, while its clean coal technology shipments totalled almost $8bn in 2013. Meanwhile, the US has called for a halt in overseas coal-fired power investment by developed nations and has cut its own funding for foreign coal projects, as have the UK, Germany, Denmark, Finland, Iceland, Norway and Sweden.

Japan, in the form of the Japan Bank for International Cooperation, is the world’s largest public funder of coal projects, investing $19.7bn between 2007 and 2013 in overseas projects according to the Natural Resources Defense Council.

Takafumi Kakudo, director for coal at Japan’s Ministry of Economy, Trade and Industry, told Reuters that “Japan is trying to help foreign countries adopt low-pollution power systems such as renewable energy and liquefied natural gas plants as much as possible. But some countries can’t afford these systems and those which produce coal want to utilize their own resources. In those cases, it is better to build plants with the high efficiency that Japan can provide.”