TOKYO (NYTIMES) - President Donald Trump has made some rocky telephone calls to other heads of state since he took office in January. But he can always count on one world leader for a good chat: Prime Minister Shinzo Abe of Japan.

Ever since the pair met in November at Trump Tower in New York just days after the presidential election, they have had a warm relationship that goes well beyond the typical partnership between two long-standing allies.

"It is very unusual," said Mitoji Yabunaka, a longtime diplomat and former vice-minister at Japan's Foreign Ministry. "It did not happen that way in the past."

Since Trump was inaugurated in January, he and Abe have met in person three times, golfed together once and talked by telephone 13 times, more than Abe spoke to President Barack Obama in his last four years in office. Over the past week alone, Abe and Trump have spoken by telephone four times.

"The president responds to Abe as a buddy and a friend," said Sheila A. Smith, a Japan expert at the Council on Foreign Relations in Washington. "And Abe has worked hard to cultivate that kind of relationship with him."

To be sure, with the North Korean nuclear crisis escalating and a missile flying directly over Japan last week, they have ample reason to chat.

But that same logic applies to South Korea, and relations between Trump and his counterpart there, President Moon Jae In, are decidedly chillier. Trump waited until the day after Sunday's (Sept 3) nuclear test in North Korea to call Moon, while he talked to Abe twice the day it happened, once before and once after the test.

Analysts sift through the terse accounts that both the White House and Abe's office release describing their conversations. The word "iron-clad" appears frequently to characterise the alliance between the two nations.

As North Korea has come to dominate the conversation, the reports inevitably include censure of the North's actions, with Trump recently saying that the United States was prepared to defend its allies "using the full range of diplomatic, conventional and nuclear capabilities at our disposal."

In talking to Trump frequently, Abe is partly ensuring that those guarantees remain in place, advisers say, given how erratic Trump can be, sometimes appearing to change policy direction between tweets. The worry is that the promises of yesterday might not hold today.

A person familiar with the thinking of Abe and his Cabinet who is not authorised to speak publicly said that given the unpredictable pronouncements from the Trump administration, Abe wants to keep in close contact to ensure there are no misunderstandings.

The Japanese news media have seized on that unpredictability.

In a morning news show on Asahi Television the day after the North's sixth nuclear test, commentators wondered how to reconcile Trump's "Talking is not the answer!" tweet from a few days earlier with comments from Secretary of State Rex Tillerson and Defence Secretary James Mattis suggesting diplomacy is still an option.

"National policy is not clear," read a graphic on the screen.

"It is still valuable to reconfirm that they have common goals and a common set of strategies or tactics," said Kunihiko Miyake, a former Japanese diplomat now teaching at Ritsumeikan University in Kyoto.

"Once is not enough. Reconfirmation should be continual and frequent. All the options are on the table. If the options are limited, you don't have to" keep talking.

Aside from the search for clarity, the telephone calls - which often coincide with calls between Japan's defence or foreign ministers and their US counterparts - reflect the alignment of two conservative and nationalistic administrations.

Although Abe had expected Hillary Clinton to win the presidential election, his Cabinet has found a more simpatico national security leadership in Trump's circle. Abe, himself a hardliner who has called for increasing Japan's military power, also appreciates the tough talk against North Korea, analysts say.

"I think the Japanese government wants to see some demonstration of American resolve," said Michael J. Green, a former Asia adviser to President George W. Bush who is now at the Center for Strategic and International Studies in Washington.

"And saber-rattling does not alarm the Japanese government as much as it does the South Korean government," which has called for more diplomatic and economic engagement with North Korea.

While other world leaders have criticised Trump for his decision to withdraw from the Paris accord on climate change and for his comments about white supremacist protests in Charlottesville, Virginia, Abe can be a safe harbour.

"Mr Abe provides him with a world leader who reaffirms Trump's own leadership and says, 'OK, I am looking to you, I am depending on you, you're the guy and I'm going to stand with you wherever you go,'" said Daniel C. Sneider, a lecturer in East Asian Studies at Stanford University. "And I think Trump needs that."

Abe stands out among world leaders for staving off censure from a president who during the campaign criticised Japanese trade barriers and suggested Japan pay a greater share of the cost of US military support.

"Abe is one of the few Asian leaders who has been able to pretty deftly navigate the unpredictability and eccentricities of Trump to his substantial advantage," said Evan S. Medeiros, who served as senior director on Asia in the National Security Council during the Obama administration.

Some critics accuse Abe of being too sycophantic in pursuit of a bromance with Trump.

But analysts say there is little to be gained by disagreeing with the president.

"It may be that President Trump is profoundly unpopular around the world," Green said. "But if you are the prime minister of Japan and you have the opportunity to shape this almost unshapeable president, it's in your national interest to do that."