North Korea moves missile 'with considerable range' to its east coast, as US troops in South are put on high alert amid rising tensions and threat of 'merciless' nuclear strike

American troops in South Korea have been placed on high alert after reports that North Korea has moved a missile with "considerable range" to its east coast.

South Korea's defence minister said this morning that the missile did not appear to be capable of hitting the the United States. He also stressed that there were no signs that Pyongyang was preparing for a full-scale conflict.

Reports in the Japanese press, later dismissed by South Korea, had suggested that the missile could be a KN-08, which is believed to be a long-range missile that if operational could hit the United States.

South Korean Defence Minister, Kim Kwan-jin, told lawmakers at a hearing that the missile's range is considerable but not far enough to hit the US mainland. He said he did not know the reasons behind the missile movement, saying it "could be for testing or drills."

This morning's news came as North Korea warned that its military had been cleared for an attack on the US using 'smaller, lighter and diversified nuclear' weapons.

US troops in South Korea were 'poised to respond' as tensions in the region continued to simmer.

Experts claim that, despite the bellicose rhetoric, North Korea has not demonstrated that it has missiles capable of long range or accuracy.

Some reports have suggested that long-range missiles unveiled by Pyongyang at a parade last year were actually mock-ups.

"From what we know of its existing inventory, North Korea has short- and medium-range missiles that could complicate a situation on the Korean Peninsula (and perhaps reach Japan), but we have not seen any evidence that it has long-range missiles that could strike the continental US, Guam or Hawaii," James Hardy, Asia Pacific editor of IHS Jane's Defence Weekly, said in a recent analysis.

Despite the continued sabre-rattling by their Northern neighbours South Korea has said there appeared to be no signs that the closed communist regime was preparing for full-blown conflict.

South Korea said there was no evidence that the North was attempting the mobilization of units including supply and rear troops.

Such moves are considered an indication that the country may be preparing for full-scale conflict.

"(North Korea's recent threats) are rhetorical threats. I believe the odds of a full-scale provocation are small," Kim Kwan-jin said.

But he added that there is still the possibility of North Korea mounting a localized, small-scale provocation against South Korea. He cited the 2010 shelling of a South Korean island, an attack that killed four people, as a possible example of such a provocation.

It emerged yesterday that the US was sending a missile shield to the Pacific island of Guam after North Korea threatened a nuclear strikes.

The Pentagon confirmed late yesterday evening that the should would be in place and ready within weeks.

Warships have already been sent to the area.

The Terminal High Altitude Area Defence System (Thaad) will be located on Guam within weeks. North Korea had previously identified the area on a list of possible targets that included the US mainland and Hawaii.

Today Prime Minister David Cameron said it would be "foolish" to abandon Britain's nuclear armed submarines amid the increased threat of an attack from North Korea.

Cameron says that the nuclear threat against Britain has risen since the Cold War's end, citing Iran and the "highly unpredictable and aggressive regime" in North Korea as "evolving threats."

Tensions in the Korean peninsula have been rising ever since the North Korean regime carried out a nuclear test in February. The United Nations voted to impose further sanctions on the country following the test.

Joint US and South Korea military drills, which included the use of B-2 stealth bombers with nuclear capability, further inflamed tensions.

For a second day today, North Korean border authorities denied entry to South Koreans who manage jointly run factories in the North Korean city of Kaesong. A North Korean government-run committee threatened to pull out North Korean workers from Kaesong as well.

Earlier this week Pyongyang announced it would restart a plutonium reactor it had shut down in 2007. A US research institute said on Wednesday that satellite imagery shows that construction needed for the restart has already begun.

North Korea's military statement today said its troops had been authorized to counter US "aggression" with "powerful practical military counteractions," including nuclear weapons.

"We formally inform the White House and Pentagon that the ever-escalating US hostile policy toward the DPRK and its reckless nuclear threat will be smashed by the strong will of all the united service personnel and people and cutting-edge smaller, lighter and diversified nuclear strike means," an unnamed spokesman from the General Bureau of the Korean People's Army said in a statement carried by state media, referring to North Korea by its formal name, the Democratic People's Republic of Korea.

US Defence Secretary Chuck Hagel said Washington is doing all it can to defuse the situation, echoing comments a day earlier by Secretary of State John Kerry.

"Some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly of our allies, starting with South Korea and Japan, and also the threats that the North Koreans have leveled directly at the United States regarding our base in Guam, threatened Hawaii, threatened the West Coast of the United States," Hagel said earlier this week.