By Jean MackenzieBBC News, Seoul

North Korean leader Kim Jong Un's reported plans to visit Russia this month have caused concern among the US and its allies.

He and President Vladimir Putin intend to discuss the possibility of North Korea providing Moscow with weapons to support its war in Ukraine, US officials say.

On the surface, an arms deal between North Korea and Russia makes perfect transactional sense.

Moscow desperately needs weapons, specifically ammunition and artillery shells, for the war in Ukraine, and Pyongyang has plenty of both.

On the other side, sanction-starved North Korea desperately needs money and food. More than three years of border closures, not to mention the breakdown of talks with the United States in 2019, have left the country more isolated than ever before.

But below the surface, it opens up the potential for Pyongyang and Moscow to start working more closely together. The US has been warning about a possible arms deal between the two countries for some time, but a leader-level meeting between Kim Jong Un and Vladimir Putin catapults this into the next realm.

While the priority for the US, certainly in the short-term, seems to be to stop North Korean weapons from getting to the frontline in Ukraine, the concern here in Seoul is over what North Korea would get in return for selling its arms to Russia.

With Russia in a desperate situation, Mr Kim will be able to extract a high price.

Perhaps he could demand increased military support from Russia. Yesterday, South Korea's intelligence service briefed that Russia's Defence Minister Sergei Shoigu had suggested Russia, China and North Korea hold joint naval drills, similar to those carried out by the US, South Korea and Japan, which Kim Jong Un so detests.

Mr Kim might also be able to call in Russian weapons in the future.

But by far the most worrying request Mr Kim could make is for Mr Putin to provide him with advanced weapons technology or knowledge, to help him make breakthroughs with his nuclear weapons programme. He is still struggling to master key strategic weapons, chiefly a spy satellite and a nuclear-armed submarine.

However officials in Seoul believe cooperation on this level is unlikely, as it could end up being strategically dangerous for Russia.

Yang Uk, a research fellow at the Asian Institute for Policy Studies, noted that even if Russia doesn't sell North Korea weapons in return, it could still fund its nuclear programme. "If Russia pays in oil and food, it can revive the North Korea economy, which in turn could then also strengthen North Korea's weapons system. It is an extra source of income for them that they didn't have."

Mr Yang, an expert in military strategy and weapons systems, added: "For 15 years we've built up a network of sanctions against North Korea, to stop it from developing and trading weapons of mass destruction. Now Russia, a permanent member of the UN Security Council, could cause this whole system to collapse."

As sanctions have been ramped up, North Korea has become increasingly dependent on China to turn a blind eye to those violating sanctions and to provide it with food aid. For the past year Beijing has refused to punish North Korea for its weapons tests at the UN Security Council, meaning it has been able to develop its nuclear arsenal without serious consequence.

North Korea provides Beijing with a useful buffer zone between itself and the US forces stationed in South Korea, meaning it pays to keep Pyongyang afloat.

But Pyongyang has always been uneasy about depending too much on China alone. With Russia on the hunt for allies, it gives Mr Kim the chance to diversify his support network.

And with Russia so desperate, the North Korean leader may feel he can wrangle even greater concessions from Moscow than he can Beijing. Mr Putin might agree to keep silent in the face of a North Korean nuclear test, whereas this could prove a step too far for Chinese President Xi Jinping.

"During the Cold War, North Korea was playing the Russians off the Chinese, very similar to how children play parents off each other," said Dr Bernard Loo of the S Rajaratnam School of International Studies in Singapore.

But there is still a question mark over whether the meeting will go ahead.

Mr Kim doesn't leave North Korea often or lightly. He is paranoid about his security and views trips abroad as fraught with danger. For his last international trips - to Hanoi to meet Donald Trump in February 2019, and to meet Mr Putin in Vladivostok in April 2019 - he rode on an armoured train. The trip to Hanoi took two long days through China.

It is unclear how private the two leaders intended their meeting to be, but it is possible the US is hoping that by making it public, it can spook Mr Kim and therefore thwart both the get-together and the potential arms deal.

Dr Loo doesn't think Mr Kim would have much wiggle room, however: "Given the reports about three-way military exercises, it would be difficult to cancel these kinds of events without everyone ending up with egg on their face."

Part of the US strategy since Russia's invasion of Ukraine has been to release intelligence to try to prevent deals from happening. North Korea and Russia have so far denied every suggestion they are looking to trade arms. Neither are likely to want this deal to be a public affair.

Additional reporting by Nicholas Yong in Singapore

ncG1vNJzZmivp6x7o67CZ5qopV%2Bjsri%2FjrCmq6SUYq60tcBmbW9vYWmCdYI%3D