Portraits of Russian President Vladimir Putin, left, and North Korean leader Kim Jong-un are seen during an official ceremony at Kim Il Sung Square to welcome Putin's state visit, Wednesday. Tass-Yonhap

China appears to be distancing itself from the growing military ties between North Korea and Russia, which now include a mutual defense pledge in the event of an attack on either nation.

Observers say that Beijing is uneasy about being framed as part of a three-way bloc with Moscow and Pyongyang, as it would complicate China's relations with Western nations.

Russian President Vladimir Putin wrapped up his 21-hour visit to Pyongyang, where he signed a new comprehensive partnership agreement with North Korean leader Kim Jong-un.

Just hours before Putin's arrival in Pyongyang early Wednesday, South Korea and China held a "two plus two" diplomatic security dialogue involving senior foreign and defense officials in Seoul, including South Korea's First Vice Foreign Minister Kim Hong-gyun and Chinese Vice Foreign Minister Sun Weidong.

The Chinese government was reportedly aware of the scheduled Kim-Putin meeting, which had been announced to the public just a day before Putin's arrival.

"The fact that the Chinese vice foreign minister came to Seoul without delaying the meeting sends a signal to North Korea. If China-North Korea relations were solid, this may not have happened," said Kang Joon-young, an expert on China at Hankuk University of Foreign Studies.

Xin Changxing, the party secretary of China's eastern Jiangsu province, made a two-day trip to Seoul from Wednesday to Thursday, marking another high-level interaction between the neighboring countries. Jiangsu boasts the second-largest economy among China's provincial governments and maintains close trade and investment ties with South Korea.

These active diplomatic engagements with South Korea could be seen as China's efforts to avoid being framed as part of a North Korea-China-Russia axis.

"China does not want to be seen as part of a North Korea-China-Russia axis against South Korea-U.S.-Japan trilateral cooperation, so it has little reason to overtly team up with the two pariah states that are under multiple international sanctions," Kang said.

He explained that for Chinese President Xi Jinping, whose top priority is economic improvement by carefully navigating the ongoing trade war with the United States and its Western allies, the formation of a three-way partnership with North Korea and Russia could be uncomfortable.

Chinese President Xi Jinping, left, and North Korean leader Kim Jong-un wave from an open top limousine as they travel along a street in Pyongyang during Xi's visit in this June 20, 2019, photo. AP-Yonhap

Some observers suspect that China does not welcome the growing military cooperation between North Korea and Russia, out of fears it could undermine China's longstanding influence over Pyongyang. While Russia's relationship with North Korea has had its ups and downs since the collapse of the Soviet Union, China has traditionally been North Korea's primary patron.

Signs of cracks in North Korea-China relations were witnessed even before the Kim-Putin summit.

Following the South Korea-Japan-China trilateral summit in Seoul on May 29, North Korea launched nearly a dozen short-range ballistic missiles into the East Sea, interpreted as a signal of frustration with China's involvement in talks discussing the denuclearization of the Korean Peninsula.

In another development, reports indicate that a "footprint tribute" commemorating a stroll between the North Korean leader and the Chinese president during the former's 2018 visit to Dalian, China, was removed recently.

The potential strain in Beijing-Pyongyang ties could present a diplomatic opportunity for Seoul in the wake of strengthening Moscow-Pyongyang ties, though the extent of China's willingness to engage in North Korean issues remains uncertain.

"South Korea may continue to persuade China that it does not need to support North Korea's attempts to recreate a Cold War-era dynamic. However, Beijing is unlikely to alter its fundamental stance on the peninsula," Kang said.

North Korean leader Kim Jong-un, left, and Russian President Vladimir Putin go for a ride in an Aurus limousine in Pyongyang, Wednesday, in this photo disclosed by the North's state media Korean Central News Agency (KCNA), Thursday. The two leaders took turns driving the Russian-built car that was presented as a gift by Putin, according to the KCNA. Yonhap