Tensions remain high on the Korean Peninsula amid reports the US has deployed an unmanned spy plane to Japan to boost its surveillance after North Korea readied missile launchers on its east coast.
The Global Hawk will be stationed at the US airbase in Misawa, northern Japan, in the first ever deployment of the aircraft in the country, the Sankei Shimbun reported, quoting government sources.
The US military informed Japan last month about plans to deploy the plane between June and September but has brought the date forward.
It comes after North Korea warned foreign diplomats they may not be safe in the country if war breaks out.
The spy plane will be stationed at the US airbase in Misawa, northern Japan Pyongyang asked foreign embassies whether they were considering evacuating staff, saying the government could not guarantee their safety in the event of conflict from April 10.
The British Foreign Office dismissed the warning as "rhetoric".
However, an urgent international effort to defuse the situation is under way.
The heads of EU missions are to meet to hammer out a common position on the crisis, while the US works its diplomatic channels to resolve the stand-off with Pyongyang.
US Secretary of State John Kerry has been holding talks with officials in South Korea, as well as China - historically North Korea's ally - to see if the Chinese can put any more pressure on North Korean leader Kim Jong-Un to back down.
Kim Jong-Un holding up a pistol as he supervises firing drills Reporting from the South Korean capital Seoul, Sky's Asia Correspondent Mark Stone, said: "In the skies above the Korean Peninsula there are spy planes operating.
"There will be drones - American drones - operating before long from a base in Japan.
"They are trying to get as much of a sense as possible of what it is that Kim Jong-Un is doing on the ground with his weaponry.
"We know he has some pretty sophisticated weaponry.
"There are artillery rounds just over the border. They could in theory hit Seoul. That's a big concern for South Korea.
"That's why they are trying to put these intelligence reports together, as well as the diplomacy behind the scenes, to try and work out what Kim Jong-Un might be up to."
A South Korean soldier looks to the north at a border observation post He continued: "The diplomats were warned by Pyongyang to leave by April 10 - no one quite knows why that date should be significant.
"It seems pretty clear, certainly speaking to western diplomats based in Pyongyang, their belief is this is just the latest round of rhetoric from North Korea.
"You would assume that if North Korea was planning some sort of war, it would actually want the diplomats from foreign countries to remain there so that they could be used as some sort of a bargaining chip - not kicked out of North Korea.
"I think it is alarming, but I think it's also probably just more rhetoric," he added.
Most governments have made it clear they have no immediate plans to withdraw personnel from the area.
A rally in support of Kim Jong-Un's order to put missiles on standby Western tourists returning from organised tours in Pyongyang - which have continued despite the crisis - said the situation on the ground appeared calm, with life going on as normal.
"We're glad to be back but we didn't feel frightened when we were there," said Tina Krabbe, from Denmark, arriving in Beijing after five days in North Korea.
The embassy warning on Friday coincided with reports that North Korea had loaded two mid-range Musudan missiles on mobile launchers and hidden them in underground facilities on its eastern coast.
The Musudan have never been tested but are believed to have a range of around 3,000km (1,860 miles), which could theoretically be pushed to 4,000km (2,485 miles).
That would cover any target in South Korea and Japan, and possibly even reach US military bases located on the Pacific island of Guam - which Pyongyang has threatened to strike.
Tensions have soared on the Korean peninsula since December, when the North test-launched a long-range rocket. In February, it conducted its third nuclear test and drew fresh UN sanctions.
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