South Korea has deployed two advanced warships off its coast as North Korea reportedly inches towards a missile launch.

The South Korean navy has dispatched two 7,600-ton Aegis class destroyers, equipped with an advanced radar system, to monitor North Korea's activities as the defiant nation has expressed its determination to press ahead with a missile launch.

The two advanced destroyers deployed on the east and west coasts have been kept on standby, suggest reports from Seoul.

"If the North fires off a missile, we will trace its trajectory," a South Korean official told the Yonhap news agency on condition of anonymity.

South Korea's ground and air forces have also been kept on high alert over the escalating tensions in the Korean Peninsula in the last few weeks.

"We are closely monitoring North Korea's missile preparations, but it is not yet clear when and where it will fire off a missile. We will step up our military posture if the North's missile affects us," defence ministry spokesperson Kim Min-seok told reporters.

South Korea's latest move has come a day after North Korea moved its missiles on its east coast targeting the US. Pyongyang is said to have given the green light for the attack.

The South Korean deployment of warships follows the defence ministry discounting Pyongyang's claim that it could be a long-range missile which can strike a target some 10,000 km away.

Defence Minister Kim Kwan-jin told the country's lawmakers that Pyongyang's missiles could strike a "considerable distance" away, reportedly pointing towards a medium-range missile.

The missile, which has a range of about 4,000 km, could potentially reach the American base in Guam in the Pacific Ocean, one of the targets mentioned by Pyongyang in its recent threats.

The US has also deployed its advanced radar system and missile shield in the base to keep track of North Korea's missile launch manoeuvres. US Defence Secretary Chuck Hagel has said that there is a "real and clear danger" from North Korea.