North Korean leader Kim Jong Un told his Chinese counterpart Xi Jinping that relations between their two countries are “unbreakable” in a letter released hours before the opening ceremony of the Beijing Winter Olympics on Friday, according to DPRK state media.

The praise-filled letter comes after North Korea conducted a record-high seven missile tests in January, including its longest-range weapon test since 2017. Several experts told NK News Chinese patience for such tests was likely waning.