North Korean soldiers have probably been killed fighting for the Kremlin on the front lines in Ukraine, South Korea has said. Kim Yong-hyun, South Korea’s defence minister, said reports that six North Korean officers were killed last week in a missile strike near Donetsk were “highly likely”.

North Korean soldiers have reportedly been killed fighting alongside Russian forces in the war in Ukraine exposing the shadowy pact between Vladimir Putin and Kim Jong Un.

North Korean leader Kim Jong-un toasted his “closest comrade” Vladimir Putin on Monday in a birthday message that claimed the countries’ deepening military alliance would make them “invincible”. The increasingly isolated Russian president turned 72 on Monday and received well-wishes from a small group of international backers,