Japan's prime minister says that the country would not involved itself in a war being fought by the US, The Washington Post reports.

“I want to make clear that Japan will never become entangled in a war being fought by the United States,” Shinzo Abe told reporters at a news conference Thursday, which was held after his government approved changes to laws governing restrictions on the Japanese self-defense forces.

"We’ve been tying to strengthen the Japan-U.S. alliance, which is the center of our country’s security," The prime minister continued. "The ties between Japan and the U.S. are much stronger than ever due to my recent visit to the US.”

Ironically, the newly approved legislation actually broadens the defensive alliance between Japan and the US. So any promise that Japan would steer clear of becoming entangled with a US war could prove impossible for Abe to keep if a conflict breaks out in the region.

And whereas the previous defensive alliance only allowed Japan to come to the military aid of the US if American assets were attacked while defending Japan, the new laws allow Tokyo to send forces to help the US after an attack even if the American forces were not currently defending Japan.

Critically, this would allow Japan to send members of its self-defense forces abroad to support US operations in another country.

Japan's post-World War II constitution, the country's self-defense forces were limited to a force that could only be used defensively or in international humanitarian missions. In the new terms, any overseas deployments would have to be approved by Japan on a case by case basis.

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The expansion of powers for the Japanese military is unprecedented, and also widely unpopular in Japan.

The new legislation allowing Japan to now send troops abroad runs counter to the majority of Japanese public opinion. In a 2013 Pew research poll, 56% of the Japanese public said they were opposed to any sort of Japanese military effort other than defense, although there was a gradual trend towards military action becoming more acceptable within the Japanese public.

The expansion of the Japanese military will also increase frictions throughout Asia. The US has recently openly mulled plans over sending naval assets to the disputed South China Sea in support of the Philippines. Beijing has said it was "extremely concerned" by the move, and a Chinese expert has said the move could lead to an escalation in the area.

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