TOKYO -- Just before 3 p.m. on Sunday, North Korean leader Kim Jong Un landed at Singapore's Changi Airport on an Air China 747 airplane provided by Beijing.

As the world awaits whether Kim and U.S. President Donald Trump will agree on denuclearization or an end to the Korean War at Tuesday's summit, Kim's use of a Chinese aircraft and the route he took to Singapore has provoked interest among China watchers. One analyst said it reflected a "tug of war" behind the scenes between Chinese President Xi Jinping and Trump.

Air China's Boeing 747s are used to carry Chinese leaders. Perhaps embarrassed by the need to have to borrow a Chinese plane, Kim avoided media exposure when he landed in Singapore and left in a long motorcade without much fanfare.

Arriving slightly later in Singapore was North Korea's official government aircraft, a Ilyushin-62M jet, jokingly referred to as "Air Force Un," which will act as a backup plane.

On Sunday evening, Trump arrived at Singapore's Paya Lebar Air Base. The president had left the contentious Group of Seven summit in Charlevoix, Quebec early, clearly not interested in the multinational dialogue.

U.S. President Donald Trump is seen upon arriving at Paya Lebar Air Base in Singapore on June 10, ahead of a summit with North Korean leader Kim Jong Un. © Reuters

Air Force One took an unexpected route to Singapore. It flew over the Atlantic and stopped over at Crete for refueling instead of flying over the Pacific with a fuel stop at a U.S. military base in Japan.

Xi had feared a situation where Kim would go "all in" with Trump, refusing any help from China. Such a move could shift the balance of power on the Korean Peninsula and squeeze China's sphere of influence.

There had been worrying indications for Beijing earlier. "We could absolutely sign an agreement," Trump said on Thursday when asked about formally ending the 1950-53 Korean War during his meeting with Kim.

The U.S. president made his remarks just after meeting Japanese Prime Minister Shinzo Abe in Washington, D.C. "We're talking about it with them, we're talking about it with a lot of other people," he said.

Over the past several days, the Chinese media has been carrying opinion pieces noting that any declaration ending the Korean War would be meaningless without the approval of one of its central participants, China. This suggested that Beijing was worried that Trump and Kim alone would conclude such a deal.

To avoid being left out, China played on Kim's fears about his safety as he headed to Singapore. Kim's plane is an old Soviet-era aircraft, which has raised questions whether it could safely make the long trip to Singapore.

Kim had tested his plane by flying to Dalian, China in early May to meet Xi. But that was a flight of only 1,000km. Singapore is 4,700km from Pyongyang. Unlike leaders of advanced countries, North Korea cannot fly an identical plane next to Air Force Un as a decoy and backup.

If China could ensure Kim's security by having him fly over Chinese airspace, perhaps escorted by Chinese fighters, or let Kim borrow a Chinese government aircraft, it would show that China remained a power behind North Korea.

While Kim's return itinerary has not been announced, having Kim travel in an Air China plane would make it easier for him to stop in Beijing on his way back to "report" about his discussions with Trump. If Trump were to leave the discussions early, as he has threatened to do, it would provide Kim with a safe passage back to his country. "Within the first minute I'll know," whether Kim is serious about a deal, Trump said when he left Canada.

If Kim had rejected China's offer of transport, things might have been trickier for Beijing. Kim could have asked that U.S. fighters stationed in South Korea, Japan or Guam to escort his plane for security. Such a flight would certainly have avoided flying over mainland China.

Furthermore, it would have been troubling if that entourage had flown over the South China Sea, much of which China claims as theirs.

So it was a small victory for Beijing when Kim chose to turn to Beijing. He must surely have reservations about being in Xi's debt, but concerns over personal security trumped any such concerns.

Chinese President Jiang Zemin, right, and his wife Wang Yeping preparing to board their plane at Thailand's resort island of Phuket in September 1999. © Reuters

When it comes to government aircraft, history offers some interesting anecdotes. Earlier this century, then-Chinese President Jiang Zemin ordered a plane to be procured for top officials. The plane was built by Boeing in the U.S. But when the plane arrived in China, it underwent a vigorous inspection that found 27 eavesdropping devices.

Similar espionage takes place between "friendly" countries such as China and North Korea. Kim's use of the Chinese plane would provide an opportunity for his conversations be heard. Beijing might also try to find out about the state of Kim's health by finding traces of DNA through lost hair.

Kim has boasted about having his finger on the nuclear button. If that were true, he would not have left his nuclear button at home. Just as the U.S. president is followed by an aide with the nuclear "football" -- a briefcase carrying the codes to launch a nuclear attack -- Kim may also have the "button" follow him around. China could analyze just how the nuclear button is handled in the reclusive state and try to capture any signals emitted from the device.

One day ahead of Kim's arrival, a North Korean advance team landed in Singapore on a Chinese chartered flight with supplies, including food for Kim.

Most experts believe that the Chinese provided their assistance free of charge.

A U.S. military aide, carrying the "football" containing the launch codes for U.S. nuclear weapons, seen at Canadian Forces Base Bagotville in La Baie, Quebec, Canada on June 8. © Reuters

The flight route that Kim took reflects a canny politician. The Air China plane took off from Pyongyang as "Flight CA122" to Beijing, but then changed its flight number to "CA61" as it headed to Singapore.

Passing over the coastline of China's southern region of Guangxi and the Bay of Tonkin, the plane carefully avoided flying within the so-called "Nine-dash line," the demarcation line that China uses to indicate its territorial claims in the South China Sea. While depending on China for security, Kim paid consideration to the U.S. and regional countries such as Vietnam and the Philippines that have disputes with China in the South China Sea.

During the weekend, Xi hosted Russian President Vladimir Putin, Iranian President Hassan Rouhani and other world leaders for the Shanghai Cooperation Organization meeting in Qingdao. With Putin and Rouhani agreeing that it was a mistake for the U.S. to pull out of the Iran deal, the whole gathering looked like an "anti-Trump" rally.

While in China, Putin rode the high-speed train from Beijing to Tianjin with Xi. China is eager to take part in Russia's high-speed railway construction, and this was an opportunity for XI to lobby Putin.

Putin invited Xi to September's Eastern Economic Forum in Vladivostok, to which Kim, Abe and South Korean President Moon Jae-in might also attend.

Russian President Vladimir Putin, left, and Chinese President Xi Jinping speak inside a train on their way from Beijing to Tianjin on June 8. © Reuters

For now, Xi has succeeded in blocking Kim from aligning himself too closely to Trump. But the tug of war between the U.S. and China will continue. The Korean Peninsula has been a battleground for great power rivalry for more than a century, with China and Russia competing with Japan and the U.S. Those tensions, for example, led to the First Sino-Japanese War of 1894 and the Russo-Japanese War of 1904 and later the Korean War.

Kim is busy weighing his options, careful not to tip the balance too far in anyone's favor, while extracting the most concessions for Pyongyang. He dined with Singaporean Prime Minister Lee Hsien Loong on Sunday evening to thank him for paying for his hotel bills.

North Korea will continue to dominate the diplomatic agenda after the historic Singapore summit is over. With Kim possibly visiting the U.N. General Assembly in New York in September, on top of a visit to Vladivostok, the regional powers of the U.S., China, South Korea, Japan and Russia will all be jostling to wield influence.