Relations between North Korea and China face a bumpy road as Pyongyang's nuclear ambitions continue to chip away at their decades-long alliance while Beijing increasingly courts Seoul for greater strategic and economic cooperation.
Their "blood alliance" born out of the 1950-53 Korean War has been eroded by Pyongyang's nuclear and missile tests and other military provocations in recent years. It suffered a major blow in December when the Kim Jong-un regime executed Jang Song-thaek, the leader's once-influential uncle who had fostered close ties with China and led joint industrial projects.
"For their ties to improve, the North should drop its byungjin line (parallel pursuit of nuclear and economic development) or at least make a commitment to freeze its nuclear programme," said Yoo Ho-yeol, a North Korea studies professor at Korea University in Seoul. "The prime sticking point is the stark gap in their positions on the nuclear issue."
Though no fundamental shift is looming in Beijing's approach, signs of a chill in their relationship have been observed.
The North's state media and officials made no mention of China as the country on Wednesday celebrated the 61st anniversary of the end of the Korean War, or what it calls the "Day of Victory in the Fatherland Liberation War." During the conflict, China dispatched up to 700,000 troops, more than 180,000 of whom were confirmed killed.
This defied its past traditions of Kim and other top officials visiting a memorial to pay respect to fallen Chinese soldiers, and official news outlets churning out articles extolling the neighbour's support and the strength of bilateral relations.
For the 60th anniversary last year, Chinese Vice President Li Yuanchao travelled to Pyongyang with a squad of veterans.
In contrast, Pyongyang's mouthpieces have been sounding a sour note toward Beijing.
The National Defence Commission, the totalitarian state's top decision-making body, backhandedly criticised China as "lacking backbone" last week for joining in the UN Security Council's condemnation of the North's recent firings of short-range ballistic missiles.
It also lashed out at Beijing after President Xi Jinping became the first Chinese leader to visit Seoul before Pyongyang early this month.
"Some backbone-lacking countries are blindly following the stinky bottom of the US, and also struggling to embrace (South Korean President) Park Geun-hye, who came to a pathetic state of being," reads the statement released by the Korean Central News Agency.
China, for its part, has been heaping pressure on its errant ally by better enforcing international sanctions, slashing economic assistance and cutting back on high-level exchanges.
China exported no crude oil to North Korea in the first five months of this year, marking the longest halt in oil supplies, Seoul's Korea Trade and Investment Promotion Agency said last month, citing data from Chinese customs authorities.
Lee Seok-hyun, vice speaker of the National Assembly and a lawmaker of the main opposition New Politics Alliance for Democracy, said after meetings with senior Chinese diplomats and officials that the North expressed Kim's wish to visit last year but Beijing declined.
"It seems that relations between China and North Korea are seriously strained and that no high-level exchanges are taking place now," he told reporters.
The ongoing diplomatic and economic squeeze represents Beijing's eroding patience in line with Pyongyang's relentless atomic development, Yoo of Korea University and other analysts said.
"With North Korea being steadfast in its nuclear ambition, any summit with Kim would be implausible for China," he told The Korea Herald.
"China would still not 'abandon' North Korea and does not need to do so. But it could try to shape the relationship into a 'normal' one by backing the regime's survival ― as far as the North doesn't escalate the situation such as through further provocations ― so that the issue will not shackle its rise to a world power down the road."
Given their strategic interdependence and upbeat trade especially along the lengthy border, however, the current iciness in Sino-North Korea ties should be confined to a temporary blip, other observers say.
One of the driving forces behind Beijing's discontent may be Kim's fickle ruling style and policy line, they say.
Whereas his late father, Jong-il, largely maintained cordial relations with China throughout his 17-year reign, the young Kim has been displaying a volatile personality and an apparent lack of diplomatic flair and strategies, making it difficult even for Beijing to deal with him.
"Aside from the fact that the relationship has not recovered since the execution of Jang, China has been reserving its support for the Kim regime since the two countries' new regimes have not yet built sufficient political trust," said Kim Keun-sik, a professor of political science and foreign affairs at Kyungnam University.
"Despite the apparent discomfort, their alliance remains robust and economic cooperation remains close, with natural resources playing a key role."