MeanwhileNorth Korea is believed to have carried out another test of a ballistic missile engine last month which failed and exploded during testing.That's according to Japanese newspaper, Asahi Shimbun, on Saturday, which adds that South Korean and U.S. officials believe it was an engine for a submarine-launched ballistic missile, or SLBM, possibly the Pukguksong-3.The failed test is said to have taken place at the eastern port city of Sinpo, home to a shipyard that makes the regime's submarines.It's reported that the explosion may have injured or even possibly killed several engineers.