Russia's Deputy Foreign Minister Andrei Rudenko visited South Korea to discuss the Ukrainian war and bilateral ties, Seoul's foreign ministry said Sunday, as the two countries trade increasingly heated rhetoric over the nuclear-armed North.Rudenko, Russia's deputy foreign minister handling Asia-Pacific affairs, met his South Korean counterpart Chung Byung-won on Friday, Seoul's foreign ministry said in a statement.Chung expressed Seoul's "grave position" on Moscow's growing military cooperation with Pyongyang and urged Russia to take "responsible actions," the statement said.His visit came the day after Moscow's Foreign Ministry spokeswoman Maria Zakharova said that heightened tension on the Korean peninsula was "primarily due to the brazen policy of the United States and its allies, including the Republic of Korea and Japan," referring to South Korea by its official name.Zakharova made the remarks when asked about South Korean President Yoon Suk Yeol's recent description of North Korea as the only country in the world that has legislated the preemptive use of nuclear weapons.Calling Yoon's remarks "blatantly biased," she also said Seoul "doesn't seem to realize that the United States' leading position is irrevocably becoming a thing of the past," and that the South "may turn out to be no more than a small bargaining chip in Washington's geopolitical games."Seoul's foreign ministry summoned Russian Ambassador Georgy Zinoviev on Saturday to protest the "rude, ignorant" comments.Since invading Ukraine in 2022, Russia has forged closer ties with Pyongyang, which South Korea and Washington accuse of shipping weapons to Moscow to help the war effort.North Korea this year declared the South its "principal enemy" and threatened war over "even 0.001 millimeters" of territorial infringement.Analysts have recently warned that North Korea could be testing cruise missiles ahead of sending them to Russia for use in Ukraine.Kim made a rare trip to Russia in September to meet President Vladimir Putin, who is set to pay a visit to Pyongyang in return.