As the Russian defence minister makes an unannounced visit to Pyongyang and Ukraine claims that North Korean troops are in Russia and ready to support Russia’s military – our Analysis Editor Ros Atkins, along with BBC Verify, has been looking at what we know about North Korea’s alleged involvement in the war.

Produced by Catherine Karelli, Richard Irvine-Brown, Vitaly Shevchenko, Olga Robinson and Jake Kwon.