Xi Jinping has told Kim Jong Un he wants to improve the relationship between China and North Korea, as the two leaders exchanged messages for the first time in more than a year and a week before US president Donald Trump arrives in China.

While Beijing has moved in recent months to clamp down on its Communist neighbour after North Korea tested a series of missiles and its biggest nuclear device to date, the US president is expected next week to press his Chinese counterpart for even tougher measures, including an oil embargo.

The letters between the Asian nations’ leaders were shorter and colder than the previous exchange in July last year, suggesting bilateral tensions remain. But while they were dry and routine, the fact they were sent at all signals that relations have not completely broken down.