"Our military detected a suspected short-range ballistic missile launched from the Pyongyang area towards the East Sea at around 22:38 today," Seoul's Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.

The JCS added the military had heightened its alert posture and was "closely sharing information regarding North Korea's ballistic missile with the United States and Japan".

Japan's defence ministry also said North Korea launched "what appears to be a ballistic missile", with its coastguard adding that it seemed to have already fallen.

Kyodo News, citing unnamed Japanese government sources, said it was a short-range missile and had fallen outside Japan's Exclusive Economic Zone.

The test comes as Seoul and Washington warned Pyongyang that any nuclear attack on the United States and South Korea would result in the end of the North Korean regime.

The two allies held their second session of the Nuclear Consultative Group in Washington on Friday, where they discussed nuclear deterrence in the event of conflict with the North.

A spokesperson for the North's defence ministry on Sunday slammed the allies' plans to expand a key annual joint military drill next year to include a nuclear operation drill and warned of "a preemptive and deadly counteraction".

"This is an open declaration on nuclear confrontation to make the use of nuclear weapons against the DPRK a fait accompli," the statement carried by the KCNA news agency said, using the official acronym for North Korea.

The missile launch also comes as Pyongyang marks the anniversary of the death of leader Kim Jong Un's father and predecessor Kim Jong Il who died on December 17, 2011.

North Korea last year declared itself an "irreversible" nuclear power and has repeatedly said it will never give up its nuclear programme, which the regime views as essential for its survival.

And last month Pyongyang successfully put a military spy satellite into orbit. It has since claimed its eye in the sky was already providing images of major US and South Korean military sites.

The UN Security Council has adopted many resolutions calling on North Korea to halt its nuclear and ballistic missile programmes since it first conducted a nuclear test in 2006.