North Korea missiles
North Korea hints at more missile launches amid impending Seoul visit by US defence chiefGetty

North Korea has hinted at more missile launches in the coming days while unilaterally declaring no-fly and no-sail zones in the East Sea as US Secretary of Defence Ashton Carter is set to visit South Korea later this week.

Seoul has said that Pyongyang has not notified them or others over the proposed launch.

Both South Korean and US forces are on high alert over the situation in the Korean Peninsula.

"North Korea has not notified the International Maritime Organisation and neighbouring countries of its declaration of the no-fly, no-sail zone. The North might have done that internally for the safety of its people on the East Coast," South Korea's defence ministry deputy spokesperson Nah Seung-yong told reporters during a routine press briefing.

The North fired four short-range missiles last week apparently in response to the ongoing joint military drills by the US and South Korea.

"No concrete, specific signs have been detected as I've just checked [the latest developments]. South Korean and the US intelligence authorities have been closely monitoring their moves around the clock," the South Korean official added.

Pyongyang often launches missiles whenever annual military exercises are conducted by US and South Korean forces in the Korean Peninsula.

The exercises, known as Foal Eagle, that began on 2 March will conclude on 24 April.

Pyongyang has always condemned the drills, dubbing them as preparations for an imminent war against North Korea. The US and South Korea say the exercises are only for defensive purposes.

North Korea also fired missiles at the start of computer-simulated military exercises early last month.