North Korean leader Kim Jong Un on Friday visited an aeronautics factory in the far-eastern Russian city of Komsomolsk-on-Amur, according to local media.
RIA Novosti news agency published footage of Kim's train arriving in the city, with a ramp and red carpet prepared for his arrival.
Russia's state-owned TASS news agency said that shortly after arriving in the city, Kim went to a plant which produces various fighter aircraft, including the Su-35 and Su-57. The aviation plant also produces civilian aircraft.
Kim arrived in Russia on Tuesday in a special armoured train before meeting President Vladimir Putin at the Vostochny Cosmodrome on Wednesday where he offered "full and unconditional support" for Russia's war in Ukraine.
How South Korea has reacted to Kim's Russia trip
Kim's visit has led to concern that Pyongyang and Moscow are looking to expand military cooperation, with speculation North Korea could provide arms in return for technology.
"We express our deep concern and regret that despite repeated warnings from the international community, North Korea and Russia discussed military cooperation issues, including satellite development," South Korea's Foreign Ministry spokesperson Lim Soo-suk said on Thursday.
US National Security Advisor Jake Sullivan held a trilateral call with counterparts from Japan and South Korea.
During talks it was noted that any arms exports from North Korea to Russia "would directly violate multiple UN Security Council resolutions, including resolutions that Russia itself voted to adopt," the White house said in a statement.
Russia-North Korea ties
Kim and Putin held a four-hour meeting earlier this week at the Vostochny Cosmodrome, the most important launchpad on Russian soil.
Kim is reportedly seeking Russia's help in developing military reconnaissance satellites.
The Kremlin confirmed on Thursday that during the talks, Putin had accepted an invitation to visit North Korea.
Spokesman Dmitry Peskov also said that Russian Foreign Minister Sergey Lavrov was expected to visit North Korea in October.
