Seoul | Behind the smiles, the balloons and the red-carpet pageantry of President Vladimir Putin's visit to North Korea last week, a strong signal came through: In the spiralling confrontation with the US and its allies over Ukraine, the Russian leader is willing to challenge Western interests like never before.

The pact that he signed with North Korean leader Kim Jong Un envisions mutual military assistance between Moscow and Pyongyang if either is attacked. Putin also announced for the first time that Russia could provide weapons to the isolated country, a move that could destabilise the Korean Peninsula and reverberate far beyond.

He described the potential arms shipments as a response to NATO allies providing Ukraine with longer-range weapons to attack Russia. He bluntly declared that Moscow has nothing to lose and is prepared to go “to the end” to achieve its goals in Ukraine.

Putin's moves added to concerns in Washington and Seoul about what they see as an alliance in which North Korea provides Moscow with badly needed munitions for its war in Ukraine in exchange for economic assistance and technology transfers that would enhance the threat posed by Kim's nuclear weapons and missile programme.

A landmark pact

The new agreement with Pyongyang marked the strongest link between Moscow and Pyongyang since the end of the Cold War.

Kim said it raised bilateral relations to the level of an alliance, while Putin was more cautious, noting the pledge of mutual military assistance mirrored a 1961 treaty between the Soviet Union and North Korea. That agreement was discarded after the Soviet collapse and replaced with a weaker one in 2000 when Putin first visited Pyongyang.

Stephen Sestanovich, senior fellow at the Council on Foreign Relations noted that when Soviet leader Nikita Khrushchev signed the deal with Pyongyang in 1961, he also tested the world's biggest nuclear bomb, built the Berlin Wall and probably started thinking about moves that led to the Cuban missile crisis in 1962.

“The question for Western policymakers now is whether Putin is becoming comparably reckless,” Sestanovich said in a commentary. “His language in North Korea -- where he denounced the United States as a worldwide 'neocolonialist dictatorship' — might make you think so.”

South Korea responded by declaring it would consider sending arms to Ukraine in a major policy change for Seoul, which so far only has sent humanitarian assistance to Kyiv under a longstanding policy of not supplying weapons to countries engaged in conflict.

Putin insisted Seoul has nothing to worry about, since the new pact only envisions military assistance in case of aggression and should act as a deterrent to prevent a conflict. He strongly warned South Korea against providing lethal weapons to Ukraine, saying it would be a “very big mistake.”

“If that happens, then we will also make corresponding decisions that will hardly please the current leadership of South Korea,” he said.

Asked whether North Korean troops could fight alongside Russian forces in Ukraine under the pact, Putin said there was no need for that.

Potential weapons for Pyongyang

Last month, Putin warned that Russia could provide long-range weapons to others to hit Western targets in response to NATO allies allowing Ukraine to use its allies' arms to make limited attacks inside Russian territory.

He followed up on that warning Thursday with an explicit threat to provide weapons to North Korea.

“I wouldn't exclude that in view of our agreements with the Democratic People's Republic of Korea,” Putin said, adding that Moscow could mirror the arguments by NATO allies that it's up to Ukraine to decide how to use Western weapons.

“We can similarly say that we supply something to somebody but have no control over what happens afterward,” Putin said. “Let them think about it.”

Sue Mi Terry, senior fellow for Korea studies at the Council on Foreign Relations, warned that Moscow could share weapons technologies with Pyongyang to help improve its ballistic missile capabilities, noting there is evidence of this happening already, with Russia possibly providing help to North Korea with its successful satellite launch in November, two months after Kim last met Putin.

“This is deeply concerning because of the substantial overlap between the technologies used for space launches and intercontinental ballistic missiles,” Terry said in a commentary. “Russia can also provide North Korea with critical help in areas where its capabilities are still nascent, such as submarine-launched ballistic missiles.”

While raising the prospect of arms supplies to Pyongyang that would violate UN sanctions, Putin also said Russia would take efforts at the world body to ease the restrictions — an apparent signal that Moscow may try to keep arms supplies to Pyongyang under the radar and maintain a degree of deniability to avoid accusations of breaching the sanctions.

Russia and North Korea have rejected assertions by the US and its allies that Pyongyang has given Moscow ballistic missiles and millions of artillery shells for use in Ukraine.

'Going to the end' in a confrontation with the West

By explicitly linking prospective arms shipments to Pyongyang to Western moves on Ukraine, Putin warned Kyiv's allies to back off as he pushes his goals in the war — or face a new round of confrontation.

“They are escalating the situation, apparently expecting that we will get scared at some point, and at the same time, they say that they want to inflict a strategic defeat on Russia on the battlefield,” Putin said.

“For Russia, it will mean an end to its statehood, an end to the millennium-long history of the Russian state. And a question arises: Why should we be afraid? Isn't it better, then, to go to the end?”

Alexander Gabuev, director of the Carnegie Russia Eurasia Centre in Berlin, said Putin's statement reflected an attempt to discourage the US and its allies from ramping up support for Kyiv as Russia pushes new offensives in several sectors of the front line.

“The situation is becoming increasingly dangerous, and Russia believes that it should quickly rap the West over its knuckles to show that its deeper engagement in the war will have a price,” he said in remarks carried by Dozhd, an independent Russian broadcaster.

He noted that Putin's statement that Moscow wouldn't know where its arms end up if sent to Pyongyang could have been a hint at North Korea's role as an arms exporter.

Treading cautiously with China

Putin's visits to North Korea handed a new challenge to Pyongyang's top ally, China, potentially allowing Kim to hedge his bets and reduce his excessive reliance on Beijing.

China so far has avoided comment on the new pact, but many experts argue that Beijing won't like losing sway over its neighbour.

Ever since Putin invaded Ukraine, Russia has come to increasingly depend on China as the main market for its energy exports and the source of high-tech technologies in the face of Western sanctions. While forging a revamped relationship with Pyongyang, the Kremlin will likely tread cautiously to avoid angering Beijing.

“Whether this upgraded Russia–North Korea relationship will be without limits depends upon China,” which will watch events closely, said Edward Howell of Chatham House in a commentary. “Beijing will have taken stern note of Kim Jong Un's claim that Russia is North Korea's 'most honest friend.' Despite the likely increase in cooperation in advanced military technology between Moscow and Pyongyang, China remains North Korea's largest economic partner.”