By Hyunsu Yim (Reuters) -North Korean leader Kim Jong Un oversaw the test-firing of the country's latest anti-aircraft missile system on Thursday, state media KCNA reported, as some experts said Pyongyang was probably getting technical help from Russia to perfect such systems.

North Korea said Friday it test-launched new anti-aircraft missiles, as its military threatened unspecified grave steps against the U.S. and South Korea over their joint military drills that it views as an invasion rehearsal.