The announcement of a first-ever summit between the United States and North Korea comes as concerning news for Japan, which has tried to set stricter conditions for dialogue with the North.

Analysts say the limits of Japan's intense lobbying of U.S. President Donald Trump have been exposed by the plan for an historic summit with North Korean leader Kim Jong Un, which looks to have been set up without Pyongyang explicitly agreeing to completely scrap its nuclear and ballistic missile programs.

Trump did not, at least publically, consult with Japanese Prime Minister Shinzo Abe before accepting the dialogue invitation from Kim, conveyed by envoys of South Korean President Moon Jae In after their trip to Pyongyang.

Tokyo-based political commentator Norio Toyoshima said Trump would have had the option of putting off accepting Kim's offer, saying he would talk with his allies before making a decision.

"But the fact that he made a phone call to Abe first right after his decision shows he does hold Abe in a certain amount of regard," Toyoshima said.

The Abe administration has been pouring energy into building close bonds with the unpredictable Trump since his inauguration, holding more than 20 telephone meetings between the leaders.

Throughout, Japan has emphasized that North Korea has only taken advantage of past efforts at dialogue, buying time to develop more dangerous weapons. It reflects the Abe administration's concerns that fresh talks with the North could lead to a compromise that does not remove the security threat to Japan.

The agreements between Kim and Moon's envoys in Pyongyang put Japan in a weaker position than it would have preferred, the analysts agreed. A mere freeze on nuclear and missile tests during a period of dialogue is not enough to reassure Tokyo, which wants the North to completely scrap the programs.

"So far we just have a statement from North Korea that it will discuss denuclearization -- it's hardly a commitment," said Leszek Buszynski, professor of international relations at Australian National University.

"I'm sure (Trump) has been advised by the State Department and people in his security establishment not to go ahead with these talks because the results may not justify the efforts," he said.

The analysts agreed the Trump-Kim talks are unlikely to yield much progress on North Korea's nuclear program, despite breaking new ground. A sitting U.S. leader has never before held a summit with a North Korean one.

Among their concerns is Trump's belief that he negotiates best on his own, despite a potential lack of understanding of the complex issues surrounding North Korea.

For starters, Washington and Pyongyang have fundamentally different views on what is meant by the denuclearization of the Korean Peninsula, said Brad Glosserman, a visiting professor at Tama University's Center for Rule-making Strategies.

Japan and the United States have said pressure in the form of sanctions will remain in place on North Korea until it moves toward its the "complete, verifiable and irreversible" denuclearization.

But the North looks unlikely to agree to that, instead aiming to at least be allowed to possess a nuclear arsenal in the vein of Pakistan, Glosserman said.

Japan, which sees the nuclear and missile technology North Korea already possesses as a threat to its security, needs to know if Trump would settle for that compromise.

What Abe can do for now is to make sure he is well informed on the policy position Trump plans to take in his talks with Kim.

Abe has an opportunity to do just that when he meets Trump on a trip to the United States next month, which he announced on Friday after his phone call with the U.S. leader.

Beyond that, Japan can continue to lean on connections in the U.S. security establishment to try to influence any U.S. plan on negotiations with the North.

Now is also the time, the analysts suggested, for the Abe administration to at least temporarily downplay its tensions with South Korea.

Trump's comments during his election campaign in 2016 raised concerns in Japan and elsewhere that the United States could trade the security of its allies for that of its homeland.

The North Korea issue, Glosserman said, has highlighted another concern -- the degree to which the United States might privilege the interest of one ally over another.

The handling of North Korea has stoked concern in Japan that South Korea is being prioritized, and vice versa, he said.

"Japan must not be perceived as anti-South Korea or anti-Korean reunification," Glosserman said, not least because South Korea is important in the enforcement of sanctions on the North.

It is particularly difficult given mistrust in Japan of Moon's intentions on North Korea and other issues.

Tokyo and Seoul have been at odds this year over how to reconcile their wartime history, particularly the issue of the "comfort women" forced into Japan's wartime military brothels.

The other thing Japan can do to try to keep its interests on the agenda in dialogue between Washington and Pyongyang is to build on its existing efforts to make an impression on Trump about North Korea's abductions of Japanese nationals in the 1970s and 1980s.

Japan should try to keep the resolution of the abduction issue a priority alongside denuclearization, while maintaining a healthy sense of skepticism about how much the talks between Trump and Kim can realistically achieve, commentator Toyoshima said.

(Satoshi Iizuka contributed to this story.)