By Ju-min Park and Jack Kim
SEOUL (Reuters) -South Korean President Yoon Suk Yeol said he would discuss with NATO leaders the distinct threat North Korea poses to Europe by deepening military ties with Russia, warning that Moscow must choose between the two Koreas where its true interests lie.
It "depends entirely" on Russia where it wants to take future ties with South Korea, Yoon said, adding that Seoul would make a decision on weapons support for Ukraine based on how a new military pact between Moscow and Pyongyang plays out.
"Military co-operation between Russia and North Korea poses a distinct threat and grave challenge to the peace and security on the Korean peninsula and in Europe," Yoon told Reuters.
The remarks came in a written response to Reuters' questions ahead of a visit to Washington for a NATO summit.
Yoon, who became the first South Korean leader to attend a NATO summit in 2022, is set to depart on Monday for the Washington event, his third time attending such a meeting.
Together with Australia, Japan and New Zealand, South Korea makes up the four Asia-Pacific partners joining in the talks on July 10 and 11.
Relations between South Korea and Russia have soured as Moscow receives shipments of ballistic missiles and artillery from Pyongyang for its war against Ukraine. Both Russia and North Korea deny such deals.
Russia has called South Korea "the most friendly among unfriendly countries", with President Vladimir Putin saying it would be making "a big mistake" if it decided to supply arms to Ukraine.
South Korea protested when Putin visited Pyongyang in June and signed a treaty with leader Kim Jong Un that covers mutual defence.
"North Korea is clearly a menace to the international society," Yoon said in his comments. "I hope that Russia will sensibly decide which side - the South or the North - is more important and necessary for its own interests."
He added, "The future of ROK-Russia relations depends entirely on Russia's actions," referring to South Korea by its official name, the Republic of Korea.
Russia said it "fully disagreed" with Yoon's comments calling on it to choose between North and South Korea.
Moscow supports building good relations with its neighbours but South Korea has imposed sanctions on Russia while North Korea is a partner, Kremlin spokesman Dmitry Peskov said in comments posted by the Russian embassy in Seoul on social media platform X on Tuesday.
Yoon has pushed for greater security ties with Europe and other U.S. allies to deter North Korea's nuclear and missile threats.
At the same time, he has looked to boost the South's role in global security, on issues such as Russia's invasion of Ukraine and rivalry between China and the United States.
ARMS FOR UKRAINE
When asked if he would authorise weapons for Ukraine, Yoon said South Korea would look at "the level and substance of military co-operation between Russia and North Korea".
That would include areas such as arms dealing, transfers of military technology and assistance with strategic materials, he added.
Russia, a permanent member of the U.N. Security Council which approved sanctions resolutions until 2017, has engaged in an "illegal" military partnership with North Korea, Yoon said, adding that it was troubling to consider what help it might be giving Pyongyang in return.
There will be a clear "negative" impact on South Korea's ties with Russia if it continues to violate U.N. resolutions, he added.
Before Russia invaded Ukraine in 2022, it was South Korea's fifth-largest export destination, while Russia was a key supplier of energy to South Korea, the Washington-based Center for Strategic and International Studies says.
South Korea will take its partnership with NATO to a new level in September, through a cyber defence exercise in which it plans to host NATO member states, organised by the country's intelligence agency, Yoon said.
Leaders are gathering in Washington for the summit of the North Atlantic Treaty Organization that will also celebrate the 75th anniversary of the military alliance.
Yoon declined to comment on possible changes to U.S. policies if Donald Trump becomes president a second time in November elections, but pointed to unwavering bipartisan support for the U.S.-South Korea alliance over the past 70 years.
"The alliance will stay strong going forward," Yoon added.
Trump's allies are assuring officials in Japan and South Korea he will support a Biden-era effort to deepen three-way ties aimed at countering China and North Korea, Reuters has reported.