"Despite its relatively low public profile as a player in the North Korea negotiations, Russia's behind-the-scenes ability to throw a wrench in the process should not be underestimated," Elizabeth Economy, director of Asia studies at the Council on Foreign Relations, said in a Thursday note.
President Vladimir Putin's government plays "a critical role as a behind-the-scenes negotiator, spoiler, and unholy ally," so it shouldn't be sidelined in nuclear negotiations, she said.
Putin has the ear of both Pyongyang and Seoul, thanks to years of steady relations with both neighbors. Moscow has attempted to play the role of honest broker in the past by promoting inter-Korean diplomacy.
Days after Russian Foreign Minister Sergei Lavrov visited North Korea last week, the Kremlin invited ruler Kim Jong Un to Moscow.
This week, Putin praised Trump's decision to hold the June 12 summit as "very brave and mature."
One of Russia's goals is constructing a liquefied natural gas pipeline in North Korea, so it can maintain its status as a major energy supplier amid rising U.S. and Australian competition, according to a recent report from analysis firm Advisor Perspectives.
Moscow has has built strong economic, cultural and commercial relations with the North in recent decades. After China, Russia is believed to hold the most economic influence over North Korea — it remains a major destination for the country's laborers, and Russian businesses are prevalent in the North's Rajin port.
"The Soviet Union helped create" modern North Korea, Artyom Lukin, deputy director for research at Vladivostok's Far Eastern Federal University, said in a November 2017 report, referring to longstanding ideological links. Moreover, "Russia remains the only country besides China that provides (North Korea) with permanent transport and telecommunications links."
Such ties underline Putin's hesitation to enforce international sanctions on the North, with reports of Russian companies continuing to export energy to the resource-poor nation.
In many ways, Russia's interests in North Korea coincide with those of China. Both want to prevent U.S. dominance in North Asia.