Russia calls for calm from all sides amid an 'explosive' mood on the Korean peninsula

Russia shares a border with North Korea and the major Pacific city of Vladivostok is less than 700km from the border. 

'Russia has to be worried as we are talking about an explosive situation in the immediate vicinity of our Far East borders,' said Deputy Foreign Minister Igor Morgulov on Wednesday.

He told Interfax: '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 warned: 'We urge all sides to refrain from any comments or actions which could further complicate the situation'.

China has also appealed for 'calm', and today summoned the ambassadors of North and South Korea, as well as the US, in Beijing. 

'We do not want to see war or turmoil break out on the peninsula, and we oppose provocative words and actions by any side', said Deputy Foreign Minister Zhang Yesui.

A day earlier US Secretary of State John Kerry denounced 'unacceptable rhetoric' emanating from North Korean leader Kim Jong-Un.

'What Kim Jong Un has been choosing to do is provocative. It is dangerous, reckless and the United States will not accept (North Korea) as a nuclear state,' he said.

The North warned it would reopen its mothballed Yongbyon reactor -- its source of weapons-grade plutonium.

UN chief Ban Ki-moon warned the situation was veering out of control and stressed 'nuclear threats are not a game'.

'The current crisis has already gone too far,' he said. 

On Wednesday North Korea blocked traffic across a heavily armed border to an industrial park it has jointly run with South Korea for the past eight years.