North Korean leader Kim Jong Un on his way home after concluding a trip to Russia's Far East

North Korean leader Kim Jong Un is on his way home Sunday from Russia, ending a six-day trip that triggered global concerns about weapons transfer deals between the two countries locked in separate standoffs with the West.

Kim began his journey back to North Korea aboard his armoured train from the Primorye region in Russia's Far East, following a farewell ceremony at a train station, Russia's state news agency RIA said.

Since entering Russia last Tuesday in his first overseas trip in more than four years, Kim had met President Vladimir Putin and visited key military and technology sites. Earlier Sunday, he was in a lighter mode, touring a university and watching a walrus show at a Russian aquarium.

Russia's state media released videos of Kim — dressed in a black suit and accompanied by his top officials — talking with Russian officials through translators as he walked through the campus of the Far Eastern Federal University in Russky Island.

Kim was later seen at the island's Primorsky Aquarium, Russia's largest, where he watched performances featuring beluga whales, bottlenose dolphins, fur seals and “Misha” the walrus, which he seemed to particularly enjoy, according to Russian media.

Kim's trip, highlighted by a summit with Putin on Wednesday, has underscored how their interests are aligning in the face of separate, intensifying confrontations with the West.

US and South Korean officials have said North Korea could provide badly needed munitions for Moscow's war on Ukraine in exchange for sophisticated Russian weapons technology that would advance Kim's nuclear ambitions.

A day after visiting an aircraft plant in Komsomolsk-on-Amur that produces Russia's most powerful fighter jets, Kim on Saturday travelled to an airport near Vladivostok, where Defence Minister Sergei Shoigu and other senior military officials gave him an up-close look at Russia's strategic bombers and other warplanes.

All the Russian warplanes shown to Kim were among the types that have seen active use in the war in Ukraine, including the Tu-160, Tu-95 and Tu-22 bombers that have regularly launched cruise missiles.

During Kim's visit, Shoigu and Lt. Gen. Sergei Kobylash, the commander of the Russian long-range bomber force, confirmed for the first time that the Tu-160 had recently received new cruise missiles with a range of more than 6,500 kilometres (over 4,040 miles).

Shoigu, who had met Kim during a rare visit to North Korea in July, also showed Kim another of Russia's latest missiles, the hypersonic Kinzhal, carried by the MiG-31 fighter jet, that saw its first combat during the war in Ukraine.

Kim and Shoigu later on Saturday traveled to Vladivostok, where they inspected the Admiral Shaposhnikov frigate. Russia's navy commander, Adm. Nikolai Yevmenov, briefed Kim on the ship's capabilities and weapons, which include long-range Kalibr cruise missiles that Russian warships have regularly fired at targets in Ukraine.

North Korea's state media reported Kim was accompanied on Saturday's visits by his top military officials, including his defense minister and the top commanders of his air force and navy.

Following a luncheon, Kim and Shoigu talked about the regional security environment and exchanged views on “practical issues arising in further strengthening the strategic and tactical coordination, cooperation and mutual exchange between the armed forces of the two countries,” according to the North's official Korean Central News Agency.

In their July meeting, Kim gave Shoigu a similar inspection of North Korean weapons systems before inviting him to a massive parade in the capital, Pyongyang, where he rolled out his most powerful intercontinental ballistic missiles designed to target the United States.

Kim's visits to military and technology sites this week possibly hint at what he wants from Russia, perhaps in exchange for supplying munitions to refill Putin's declining reserves as his invasion of Ukraine becomes a drawn-out war of attrition.

Kim's meeting with Putin was held at Russia's main spaceport, a location that pointed to his desire for Russian assistance in his efforts to acquire space-based reconnaissance assets and missile technologies.

Experts have said potential military cooperation between the countries could include efforts to modernise North Korea's outdated air force, which relies on warplanes sent from the Soviet Union in the 1980s.