US Defense Secretary Ash Carter (right) and Japan's Defense Minister Gen Nakatani speak during a press conference at the Defense Ministry in Tokyo on Wednesday. Photo: AP

Analysts have interpreted the revision of US-Japan defense guidelines as an official endorsement from the US to allow Japan to exercise the right of collective self-defense, a step further in Japan's efforts to use military force overseas even when it is not under attack.

"The new [US-Japan defense] guidelines will transform the US-Japan alliance, expanding opportunities for the US armed forces and the Japan Self-Defense Forces to cooperate seamlessly," US Defense Secretary Ashton Carton told reporters on Wednesday in Tokyo after meeting with his Japanese counterpart Gen Nakatani.

"The US supports Japan's efforts to play a more proactive role in contributing to regional peace and security," Carter said, adding that the two governments would cooperate "around the globe," according to Bloomberg news agency.

"The term of 'seamless cooperation' indicates that there will be no restraints on what measure Japan takes to cooperate with the US military-wise, be it finance, arms or combat personnel," Zhou Yongsheng, a professor of international relations at China Foreign Affairs University, told the Global Times.

Geng Xin, a research fellow from the Chongyang Institute of Financial Studies under Renmin University of China, said the move signals that US-Japan security cooperation has entered a new phase as Japan's role in US global strategy and military actions is expected to significantly increase.

The new revision of the guidelines, the first in 18 years, is scheduled to be completed in the coming weeks. Japanese Prime Minister Shinzo Abe is about to embark on an official visit to Washington DC at the end of this month.

He is expected to confirm the guidelines with US President Barack Obama to clear the legal hurdles in order for Japan to revise a series of security-related bills in May.

In the revised guidelines, the US and Japan will state how their forces will cooperate in four specific situations, including a case of collective self-defense, Kyodo News quoted anonymous Japanese government sources as saying.

The first situation covers peacetime and "gray zone" incidents that stop short of military attacks on Japan. The second covers incidents that would significantly influence Japan's peace and security and is expected to pave the way for Japan to provide ammunition and refuel warplanes bound for combat zones.

The third covers incidents that pose a clear danger to Japan's existence due to an armed attack on an allied country. The fourth is a direct attack on Japan.

"The categories listed in the revised guidelines very much overlap with the concept of collective self-defense. Although the US has on several occasions voiced its support, the new guidelines can be interpreted as an official US endorsement of Japan exercising such rights, written down and signed on paper," Geng told the Global Times.

In the joint press conference on Wednesday, Nakatani said the new guidelines will not be aimed at particular geographical regions, but analysts have interpreted them as a gesture with an eye to China.

"It's clear that Carter had China in his mind when he embarked on his first Asia tour, visiting Japan and South Korea, two important neighbors of China," a professor from Japan's Kyushu University, who demanded anonymity, told the Global Times.

On Wednesday, Carter hailed the revision as a move to "allow us to open up many new opportunities to strengthen the alliance in areas where that strengthening is needed, because the security situation has changed."

"The US is concerned about China's increasing military prowess," the professor said. "One of Carter's missions is to upgrade the US-Japan alliance to a new level as part of his country's effort to achieve US pivot to Asia."

Analysts also warned that the move could have a strong influence on regional politics and, in the worst case, touch off a new arms race in East Asia.

"China, Russia, South and North Korea as well as some Southeast Asian countries will all grow alert if constraints on Japan's Self-Defense Force are lifted. The US, as well, will risk further alienating South Korea from its current US-Japan-South Korea alliance," Geng said.

Japan's current constitution, which was made in 1947 under the supervision of the US, states that "the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes."

The Abe administration last July announced its decision to reinterpret Japan's pacifist constitution to loosen restraints on the self-defense role of its military.

The move is not necessarily popular among the Japanese public. A poll released by the Pew Research Center on Tuesday showed that only 23 percent of Japanese believe Japan should play a more active military role in regional affairs.

Jiang Feng contributed to this story