Russia has promised Putin will visit North Korea after hosting its leader Kim Jong Un in the Russian Far East last September.

South Korean and United States officials have warned that Russian President Vladimir Putin’s visit to North Korea, which could take place this month and deepen military ties, would be a breach of United Nations Security Council resolutions.

According to Seoul’s foreign ministry on Friday, Vice Foreign Minister Kim Hong-kyun said in an emergency phone call with US Deputy Secretary of State Kurt Campbell that Putin’s visit should not result in more military cooperation between Moscow and Pyongyang.

“While closely monitoring related developments, the two sides agreed to resolutely respond through airtight cooperation to North Korea’s provocations against South Korea and actions that escalate tensions in the region,” the ministry said in a statement.

Campbell also pledged continued cooperation to tackle potential regional instability and challenges caused by the visit.

Rumours about the trip began on Monday after Russia’s Vedomosti newspaper reported that Putin would visit North Korea and Vietnam in the coming weeks.

On Thursday, Kremlin spokesperson Dmitry Peskov declined to give a date for the possible visit.

“We have the right to develop good relations with our neighbours and this should not cause concern for anyone,” Peskov said.

He added North Korea was a “friendly country for us, with whom we are developing bilateral relations”.

“We will do that further. The potential for development in our relations is very deep”.

Weapons to target Ukraine

The US has claimed that during Russia’s war with Ukraine, North Korean-made missiles and artillery shells have been used to attack Ukraine.

While Moscow and Pyongyang have denied the claims, the two leaders met in eastern Russia last September and agreed to deepen cooperation, including military relations.

On Wednesday, Campbell said the US has a good understanding of what North Korea has provided Russia, adding that it has had “a substantial impact on the battlefield”.

But what’s less clear, he said, was what Russia had given its counterpart.

“Hard currency? Is it energy? Is it capabilities that allow them to advance their nuclear or missile products? We don’t know. But we’re concerned by that and watching carefully,” he said.

In March, US Director of National Intelligence Avril Haines said due to the war on Ukraine, Russia had been forced to grant “long-sought concessions” to North Korea, China and Iran “with the potential to undermine, among other things, long-held non-proliferation norms”.

While Haines did not elaborate on her statement, the reference to non-proliferation norms was a potential warning that Russia could provide North Korea with military-related technology.

Kim has been leading the modernisation of North Korea’s military arsenal, with the country testing an array of weaponry and last November putting its first military spy satellite into orbit.