The artillery shells were sent to Russia through ships and other transport means since early August, said lawmaker Yoo Sang-bum, citing an intelligence briefing.
The short-range arms will last for about two months, he said.
The South Korean National Intelligence Service (NIS), which held the briefing, also believes the Kim Jong-un regime is operating its munitions factories at full capacity to meet Moscow’s arms demands.
The hermit kingdom is also mobilising its citizens to increase production, the South Korean lawmaker said.
North Korea also likely dispatched weapons experts to Russia in October to counsel Moscow’s officials on how to use the weapons.
The signs of increased partnership come shortly after Mr Putin and Mr Kim met in east Russia in September, igniting speculation that North Korea will soon assist Moscow in its continuing invasion of Ukraine.
The US and South Korea have speculated that the two nations have entered an arms arrangement to provide Russia with badly needed munitions in exchange for advanced Russian technologies that can strengthen North Korea’s nuclear-armed military.
Experts also pointed out that the two leaders’ much-publicised meeting at Russia’s Vostochny Cosmodrome, a major satellite launch facility, was a sign that Mr Kim seeks Russian technology assistance for its spy satellite programme.
They said such a quid pro quo arrangement between the countries can help Russia rebuild its artillery stock without facing a lull on the battlefield in Ukraine.
Pyongyang and Moscow have, however, rejected claims by the US and South Korea.
Officials in South Korea are concerned the arrangement could benefit North Korea with sensitive Russian technologies and boost Mr Kim’s nuclear weapons and missiles programme.
The NIS believes it is more likely that Russia’s help will be limited to conventional capabilities, possibly to help North Korea improve its ageing fighter aircraft fleet, Mr Yoo said.
He said North Korea is possibly getting Russia’s technological help for a military reconnaissance satellite after consecutive launch failures.
The North’s latest attempt at launching a spy satellite in October had failed to materialise.
Mr Yoo said the South Korean spy agency believes North Korea is now in its final phase of preparations for the third launch of the spy satellite which is more likely to be successful.
In a joint statement, the US, South Korea and Japan strongly condemned what they described as North Korea’s supply of munitions and military equipment to Russia, saying such weapons shipments sharply increase the human toll of Russia’s aggression in Ukraine.
It came days after Russian foreign minister Sergei Lavrov rejected US claims that his country received munitions from North Korea as he returned from a two-day trip to Pyongyang.
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