N. Korea imposes 'no-fly, no-sail zones off both coasts'

North Korea has imposed no-fly and no-sail zones off both its coasts, South Korean government sources tell Yonhap news agency.

The move indicates that Pyongyang intends to conduct major military drills and the test-firing of short-to-medium range missiles also remains a possibility, South Korea's Yonhap news agency said on Wednesday.

"The North's military ... is preparing large-scale combined military exercises so it may have blocked off the areas for nautical firing or fighter jet firing exercises," Yonhap quoted a South Korean government source as saying.

"But the firing of missiles cannot be ruled out."

The agency also reported that North Korea has already begun submarine drills as it steps up preparations for nationwide military exercises.

In February, Kim Min-seok, a South Korean ministry spokesman said a large-scale military drill was likely to be held in the North due to the unusually high levels of participation by the North's artillery, special forces and air force over the winter months.

The report follows Pyongyang's threat to scrap a ceasefire which ended the 1950-53 Korean War due to an ongoing military US-South Korean military drill. The North further said it will cut off a military phone line in the truce village of Panmunjom.

On Wednesday the South Korean military issued an uncharacteristically harsh warning, saying it would strike the North’s command leadership if provoked.  

"If North Korea attempts a provocation that threatens the lives and security of our people, our military will forcefully and decisively strike not only the origin of provocation and its supporting forces, but also its command leadership," said Maj. Gen. Kim Yong-hyun, chief operations officer at the military’s Office of Joint Chiefs of Staff. "We make it clear that we are all prepared."

Building tensions on the Korean Peninsula come as the 15-nation UN Security Council prepares to ‘significantly expand’ sanctions on North Korea over a third nuclear test conducted in February.

Several UN envoys said on Tuesday that a vote on the draft sanctions resolution agreed upon by Washington and Beijing was expected on Thursday.

The sanctions would explicitly ban the sale of luxury goods which are a regular staple of North Korea’s ruling elite and make it more difficult for Pyongyang to transfer funds globally, a council diplomat told Reuters on condition of anonymity.