A TV screen in a South Korean railway station showing a North Korean military parade.AP Photo/Ahn Young-joonThe US says North Korean troops are in Russia, possibly bound for the war in Ukraine.The soldiers face strict measures to prevent their desertion, North Korea experts say.The country uses a rigid system and family hostages to ensure loyalty.Any North Korean troops sent to fight in Ukraine would be subject to harsh measures to ensure they don't desert, observers have told Business Insider.There are growing reports of a mass North Korean deployment in support of Russian troops.On Wednesday, the US defense secretary, Lloyd Austin, said "there is evidence" that North Korean troops are training in Russia.Scattered reports have said smaller numbers of North Korean troops are already in Ukraine.The Ukrainian outlets Suspilne and Hromadske reported some early desertions, citing anonymous sources.Business Insider couldn't independently confirm the reports, and Ukraine's military-defense agency didn't respond to a request for comment.A tight leashCommitting large numbers of troops abroad is risky for Kim Jong Un, who oversees a totalitarian state that rarely lets people out.But the prize for cooperating with Russia is great — technological advancement and help for North Korea's cash-strapped economy.Joseph S.