North Korea fired what it claims to be a "space launch vehicle" southward Thursday, the South Korean military said, in an apparent second try to put a spy satellite into orbit less than three months after its first failed attempt.

Japan's top government spokesman said on Monday that the country would be on the lookout for any launch by North Korea.

Nuclear-armed North Korea test-fired two strategic cruise missiles from a submarine, just as US-South Korea military drills were due to begin.

Fhe South Korean military said that, North Korea fired three ballistic missiles toward the sea east of the Korean Peninsula.

N. Korea intends to have the world’s most powerful nuclear force as he promoted dozens of military officers involved in the recent launch of a new ballistic missile, North Korean leader Kim Jong Un said.

State media KCNA said that, North Korean leader pledged to counter US nuclear threats with nuclear weapons as he inspected a test of the country’s new intercontinental ballistic missile (ICBM).

"Our missile tests are for self-defence against direct US military threats and they have not harmed the safety of neighbouring countries and regions". North Korea said.

Chinese President Xi Jinping will visit North Korea for a two-day visit starting this Thursday, according to Chinese state media reports.