As North Korea's saber-rattling reached a fever pitch on Thursday, several countries, including the North's ally, China, expressed concern about the hermit kingdom's increasingly heated rhetoric.
A Chinese diplomat reportedly met with ambassadors from the United States, and North and South Korea to express "serious concern" over the situation in the Korean Peninsula.
"In the present situation, China believes all sides must remain calm and exercise restraint and not take actions which are mutually provocative and must certainly not take actions which will worsen the situation," Chinese Foreign Ministry spokesman Hong Lei said on Wednesday.
Chinese warships conducted live-firing drills in the West Sea, where South Korea and United States forces were holding a joint military exercise, according to reports from the official Chinese newspaper Global Times, cited by South Korean news site Chosun Ilbo.
Chinese forces have reportedly been at the highest level of alert since March 19.
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"Large groups of soldiers were seen on the streets in Ji'an, a city in Jilin, amid reports that the [Army] had been ordered to combat readiness status," Global Times said. "Heavy armored vehicles, including tanks and armored personnel carriers, were reported moving near the Yalu [Apnok] River that separates China from North Korea."
"Whenever the crisis deepened on the Korean Peninsula, since the North's second nuclear test in 2009, China has reinforced its troops along the border. Amid escalating threats from North Korea, it's highly likely that Army has moved troops from the Shenyang Military Region," a diplomatic source in Beijing said, according to Chosun Ilbo.
China's reaction to the Korea crisis is especially important, because a treaty signed half a century ago obliges China to “render military and other assistance by all means at its disposal” in the event North Korea comes under “armed attack by any state.”
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The other powerful international player in the region, Russia, also said it was worried about the "explosive" situation on the Korean Peninsula.
"Russia has to be worried as we are talking about an explosive situation in the immediate vicinity of our Far East borders," Deputy Foreign Minister Igor Morgulov told the Interfax news agency.
"In the current tense atmosphere, it would only need an elementary human error or technical problem for the situation to go out of control and plunge into a critical dive," he added.
"We urge all sides to refrain from any comments or actions which could further complicate the situation," Morgulov said. Russia shares a small part of its border with North Korea in the Far Eastern region.
Even faraway France has expressed its concern, urging the North to "quickly resume the path of dialogue" and refrain from "further provocation," according to Chinese newspaper Xinhua, which quoted Philippe Lalliot, France's spokesperson for foreign affairs.
The United Kingdom's Prime Minister David Cameron called the North's nuclear threats a "real concern" on Thursday, while speaking to defense industry workers in Scotland.
"North Korea does now have missile technology that is able to reach the whole of the US," he said, according to Bloomberg. "If so they can reach Europe and us too."
Cameron also made a case for the UK having submarines that carry Trident nuclear missiles, citing North Korea as one of the potential threats in the world.
Writing in The Daily Telegraph, Cameron said, "...the highly unpredictable and aggressive regime in North Korea recently conducted its third nuclear test and could already have enough fissile material to produce more than a dozen nuclear weapons. Last year North Korea unveiled a long-range ballistic missile which it claims can reach the whole of the United States. If this became a reality it would also affect the whole of Europe, including the UK."