North Korean leader Kim Jong Un has overseen drills simulating a nuclear counterattack against the U.S. and South Korea in a warning to the allies who are scaling up their joint military exercises, state media KCNA said on Monday.

The North's drills involved a short-range missile launch but - unusually - the missile flew from a buried silo, which analysts say would help improve speed and stability in future tests of intercontinental ballistic missiles (ICBM).

KCNA said the exercises on Saturday and Sunday were designed to boost the country's "war deterrence and nuclear counterattack capability".