Electricity bills have soared across Japan since energy costs rocketed temporarily following the start of the Russian invasion of Ukraine nearly a year ago.

The energy situation is driven partly by European nations seeking to pivot their energy sources from Russia to other parts of the world.

Japan relies on imports to meet most of its demand for liquefied natural gas, or LNG, a major energy source for thermal power plants.

The Japan Korea Marker, or JKM, is a benchmark index for spot prices of LNG cargo to East Asia including Japan.

The index stood at some 20 dollars per one million British thermal units before the invasion began on February 24 last year.

But it soared to a record 84.7 dollars per million Btu in March. It also topped 70 dollars last August in response to a rise in energy demand.

The index has since dropped and is currently below levels seen before the start of the Russian invasion. But last year's surges are pushing up electricity bills across Japan.

Many households across the country subscribe to major utility firms under plans that cap how much the companies can pass on energy cost rises to consumers.

All of Japan's 10 major electricity providers have raised their power bills as much as they can under government regulations. Seven of them have applied for regulatory approval to increase their rates above the ceilings from April or later.

Roughly 9 percent of LNG imports to Japan comes from Russia in terms of volume.

Two Japanese trading houses retain stakes in the oil and gas project Sakhalin-2 in the Russian Far East despite international sanctions against Moscow for the invasion.

But there are strong concerns about whether Japan will be able to continue securing sufficient amounts of LNG as it remains uncertain how Russia will act.