US President Joe Biden said Friday he is under "no illusions" about the difficulty of convincing North Korea to give up its nuclear arsenal, after White House talks with his South Korean counterpart Moon Jae-in. "We're under no illusions how difficult this is -- none whatsoever. The past four administrations have not achieved the objective. It's an incredibly difficult objective," Biden told reporters at a joint press conference with Moon. The US leader announced he had named veteran diplomat Sung Kim, the former US ambassador to Seoul, as his special envoy to Pyongyang. sms-sst/ec