"I think it's because of the money," he said, adding: "I think North Korea is very poor, so they will send their people to the front."Russian President Vladimir Putin and North Korean dictator Kim Jong-Un signed a security agreement, pledging to provide aid to one another if either is attacked.With Russia's military stocks running low and domestic production capacity simultaneously hampered by Western sanctions, North Korea has been shaping up to be Russia's leading weapons supplier.Moscow has reportedly received extensive military packages from Pyongyang, including ballistic missiles and millions of artillery shells.The financial details of the arrangement have not been made public, but in exchange for ammunition already supplied, Russia has reportedly provided North Korea with technology to help it deploy spy satellites as well as tanks and aircraft.Zelensky also said he believed North Korean troops would struggle to operate effectively while fighting for Russia.