China virtually halted exports of petroleum products, coal, and other key materials to North Korea in the months leading to this week’s unprecedented summit between Kim Jong Un, the North Korean leader, and his Chinese counterpart Xi Jinping. The export freeze — revealed in official Chinese data and going much further than the limits stipulated under UN sanctions — shows the extent of Chinese pressure following the ramping up of Pyongyang’s nuclear testing programme. It also suggests that behind Mr. Xi’s talk this week of a “profound revolutionary friendship” between the two nations, his government has been playing hardball with its neighbor.

“China has effectively turned off the petroleum taps flowing into North Korea,” said Alex Wolf, an economist at Aberdeen Standard Investments and a former US diplomat in China. “From the data available . . . it appears that the North Korean economy is under a great deal of pressure and this has undoubtedly contributed to North Korea’s change in policy. “It is Chinese ‘maximum pressure’ that may be bringing a change in North Korean policy.” Since its September test of a nuclear weapon, North Korea has launched a highly unusual series of diplomatic forays. Mr Kim’s sister, Kim Yo Jung, was dispatched to the Winter Olympics held in South Korea in February. Mr Kim then shocked many by inviting Donald Trump to a summit — an offer that the US president accepted. Following the visit to Beijing this week, North and South Korea announced a historic summit scheduled for later this month.