Japan's Mitsubishi and Mitsui said Wednesday they will import liquefied natural gas (LNG) from the United States, amid a push to boost energy sources after last year's nuclear crisis.

The country's two largest trading companies said they would each order 4.0 million tonnes of the gas annually from Cameron LNG, a unit of Sempra Energy, as early as 2016, reportedly the first such deal between Japan and the US.

The deal comes as Japan pushes to boost new energy sources amid strong public opposition to restarting the country's atomic reactors after the March quake-tsunami disaster sparked the worst nuclear accident in a generation.

Resource-poor Japan and South Korea are the world's top LNG importers, accounting for nearly half of all shipments.

Last week, Mitsubishi said it was in talks with Royal Dutch Shell as well as a Chinese and a South Korean firm to produce liquefied natural gas in Western Canada, in a deal reportedly worth more than $12.0 billion.

On Wednesday, Mitsubishi said it had agreed to "procure 4.0 million tonnes annually from the North American natural gas market... processed through the Cameron LNG facility".

A Mitsubishi spokesman said the firm will then sell the gas, which is temporarily liquefied for easier storage and transportation, to utility customers in Japan and other parts of Asia.

"Under a situation where Japan is currently importing LNG mainly from the Middle East and Southeast Asia, LNG import from the United States will contribute to diversification of energy resources and increase flexibility of supply plans," Mitsubishi said.

A Mitsui spokesman confirmed the trader will buy 4.0 million tonnes of the liquefied gas from Cameron's facility in the southern US state of Louisiana.