North Korean leader Kim Jong Un visited a nuclear submarine factory and received a message from Russia’s Vladimir Putin hailing the countries’ “invincible friendship,” state media said Thursday.North Korea and Russia have drawn closer since Moscow launched its full-scale invasion of Ukraine nearly four years ago, and Pyongyang has sent troops to fight and die for Russia.In return, Russia is sending North Korea financial aid, military technology and food and energy supplies, analysts say.The “heroic” efforts of North Korean soldiers in Russia’s Kursk region “clearly proved the invincible friendship” between Moscow and Pyongyang, Putin said in a message to Kim, according to the Korean Central News Agency (KCNA).For all the latest headlines, follow our Google News channel online or via the app.Their work demonstrated the nations’ “militant fraternity,” Putin said in the message received by Pyongyang last week.The provisions of the “historic treaty” the two leaders signed last year, which