Nikolai Patrushev, the secretary of the Kremlin's powerful security council, said Russia was concerned about Pyongyang's rising atomic "potential".
"It certainly causes concern all over the world – and in our country too," he said.
"We border them, and in fact we cannot but be perplexed when they improve their missile technology (and) nuclear potential….It worries us."
Nikolai Patrushev was concerned about Pyongyang's rising atomic "potential"
They see that they are being isolated, that they must ensure their security on their own
But the former FSB security service chief warned North Korea "should not be provoked" into a siege mentality and a deadly arms build-up – yet this "is what is going on".
The Putin ultra-loyalist warned the West: "They see that they are being isolated, that they must ensure their security on their own.
"They will not be assisted in that regard.
Mr Patrushev called for multinational talks
"They see threats for themselves."
Mr Patrushev called for multinational talks.
"It is not easy, but we need to strive for this, to negotiate with North Korea," he said.
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Tensions on the Korean Peninsula have been rising
VOLCANO: North Korea nuclear weapons could lead to ERUPTION
Fri, May 19, 2017
A new problem may erupt: when North Korea tests a nuclear weapon, specialists say the energy could trigger a volcanic eruption in Paektu. That could be a huge disaster, killing thousands in North Korea and on the Chinese side too.
Eric Lafforgue/Exclusivepix Medi
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Paektu is an active volcano which last erupted in 1903
The West must be open to "understanding the concerns that they have as well", he said.
Tensions on the Korean Peninsula have been rising since early 2016 when North Korea conducted a nuclear test and then launched a ballistic missile carrying a satellite.
In September 2016, Pyongyang conducted another nuclear test, and more than 20 missiles were test-fired during the year.
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North Korea fired a ballistic missile on May 14
On May 14, North Korea fired a ballistic missile from the area north-west of the town of Kusong.
According to Japan, the missile flew about 800 km and fell in the sea outside Tokyo's exclusive economic zone.