Japan's policy on North Korea has been coming under increasing scrutiny, particularly after Prime Minister Shinzo Abe expressed willingness to hold a summit with North Korean leader Kim Jong Un "without conditions."

Since Pyongyang fired projectiles that appeared to be short-range ballistic missiles on May 4 and 9, Japan has taken a tougher stance against North Korea than the United States, claiming the missile and nuclear threat remains unchanged in the region.

Some Japanese government officials, however, have become concerned that as long as Tokyo continues to put up a strong front against Pyongyang, a summit between Abe and Workers' Party of Korea Chairman Kim will not eventuate.

Japan has also been at odds with the United States over how to address North Korea's recent launches of short-range missiles, raising fears that Abe's government is not necessarily working in tandem with the U.S. administration of President Donald Trump.

"We need to remind ourselves of the undeniable fact that there has been no essential change in North Korea's nuclear and missile capacities," Japanese Defense Minister Takeshi Iwaya said in a speech at the Asia Security Summit in Singapore on Saturday.

"North Korea's launching of short-range ballistic missiles at the beginning of May, which violated relevant United Nations Security Council resolutions, is extremely regrettable," Iwaya added at the gathering, known as the Shangri-La Dialogue.

His remarks came less than a week after Trump said at a joint press conference with Abe in Tokyo late last month, "My people think it could have been a violation, as you know. I view it differently."

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Trump -- who has voiced eagerness to continue talks with Kim even after the collapse of their Feb. 27-28 summit in Hanoi -- has apparently been trying to put the matter to rest in order to not provoke North Korea, foreign affairs experts say.

A diplomatic source told Kyodo News, "I cannot understand why Japan has lambasted North Korea, using relatively strong expressions. Does Abe really want to meet with Kim Jong Un?"

Although Abe had indicated a future summit with Kim would not be possible without a guarantee of progress, he said in early May, "I myself need to face Chairman Kim without conditions" to resolve several bilateral issues.

But Abe's government has not started to make conciliatory gestures toward Pyongyang, while North Korea has shown no sign of rapprochement with Japan.

"Anti-Japanese sentiment has been spreading in North Korea. It is difficult to imagine that Abe and Kim will sit at the same table in the near future," a source familiar with the situation in Pyongyang said.

A Japanese government official said, "We know that our hard-line approach to North Korea may lower the possibility of Prime Minister Abe's meeting with Chairman Kim, but in terms of security, we cannot easily let down our guard against North Korea."

Sounding a note of caution about Trump's kid-gloves approach to North Korea, another government official said, "It is unclear whether the president and Prime Minister Abe are sharing the same view about the denuclearization issue."

"If the United States really thinks it is OK unless North Korea fires intercontinental ballistic missiles capable of reaching the U.S. continent, we may have to reconsider how to cooperate with the Trump administration over the North Korea issue," the official said.