North Korean leader Kim Jong-un on Tuesday arrived in Russia to meet President Vladimir Putin, media reports said.
Kim, who last visited Russia in 2019, arrived in the Russian border city of Khasan, and is on his way to the Far Eastern city of Ussuriysk, according to Yonhap news agency.
He left the capital Pyongyang on his private train late Sunday along with senior government officials and military personnel, North Korean state media said.
South Korean Defense Ministry spokesman Jeon Ha-kyou said Seoul is closely monitoring the visit and possible talks between the two countries over arms trade.
"Considering that a large number of military personnel is accompanying him, (we) are closely monitoring whether negotiations over arms trade between North Korea and Russia, and technology transfers will take place," he said.
Earlier, the US claimed secretive talks between Russia and North Korea to supply the Kremlin with munitions for its war effort in Ukraine were "actively advancing."
Putin is in Vladivostok for the Eastern Economic Forum, and is expected to speak at a plenary session on Tuesday.