The United States says it is taking "all necessary precautions" after North Korea rang fresh alarms in an escalating crisis by moving a medium-range missile to its east coast.
South Korea's Defence Minister, Kim Kwan Jin, said the missile could reach a "considerable distance", but not the US mainland, telling MPs it "could be aimed at test-firing or military drills".
It was the latest incremental move by North Korea which, incensed at fresh United Nations sanctions and South Korea-US military drills, has issued a series of apocalyptic threats of nuclear war in recent weeks.
White House spokesman Jay Carney yesterday said the barrage of threats fitted a "regrettable but familiar" pattern of North Korean behaviour.
"We're taking all the necessary precautions," Carney said, citing "prudent measures" to respond to the possible missile threat.
The Pentagon has said it will send missile-interceptor batteries to protect bases on Guam, a US territory 3380km southeast of North Korea and home to 6000 American military personnel.
South Korean intelligence sources reportedly identified the North Korean missile as an intermediate-range Musudan.
The Musudan has never been tested, but is believed to have a range of around 3000km, which could theoretically be pushed to 4000km with a light payload.
South Korea's Defence Ministry spokesman said he could not confirm the precise type of missile, but said a Musudan could pose a threat to US forces on Guam.
Most experts think the North is not yet capable of mounting a nuclear device on a ballistic missile capable of striking US bases or territory.
On Thursday the North Korean army said it had approval for military action, possibly involving "diversified" nuclear weapons, against the threat posed by US B-52 and B-2 stealth bombers participating in military drills with South Korea.
'The moment of explosion is approaching fast," the army's general staff said.
The blistering rhetoric has stoked international concern, with UN chief Ban Ki-moon describing the daily threats from Pyongyang as "really alarming and troubling".
"I think they have gone too far in their rhetoric and I am concerned that if by any misjudgment, by any miscalculations ... this will have very serious implications," Ban said.
Australian Prime Minister Julia Gillard expressed solidarity with South Korea in a phone hook-up with President Park Geun Hye.
She emphasised the importance Australia placed on South Korea's security and promised to continue pressuring North Korea to put an end to its stance, and to engage in dialogue with its southern neighbour.
Australian Foreign Minister Bob Carr has said he would make a personal appeal for China to persuade North Korea to "ratchet down" its behaviour.
US Defence Secretary Chuck Hagel has said the threat levels combined with the North's military capabilities represented a "real and clear danger" to the US and its allies, South Korea and Japan.
Since the movement of the North Korean missile, there has been speculation Pyongyang might schedule a firing to coincide with the birthday of the country's late founder Kim Il Sung in mid-April.
A provocative missile test fired into the sea over Japan is one scenario that analysts have said the North could choose to exit the crisis with a face-saving show of force.
"A flight test would make sense," said Daniel Pinkston, a North Korea expert at the International Crisis Group.
"But I'd be surprised if they used an untested missile. At this stage in the game, they don't want to be firing off something that might disintegrate after 30 seconds," Pinkston said.
Apart from its threats of nuclear attack, the North also warned this week it would reopen its mothballed Yongbyon reactor - its source of weapons-grade plutonium that was closed in 2007 under an aid-for-disarmament accord.
On Thursday, North Korea blocked access to its Kaesong joint industrial zone with South Korea for the second day running, and threatened to pull out its 53,000 workers in a furious reaction to the South's airing of a "military" contingency plan to protect its own workers there.
The zone was shut yesterday for a scheduled North Korean holiday, with managers of the 123 South Korean companies in the complex warning they would have to close down operations in a matter of days unless the North lifted the ban on incoming raw materials and personnel.