Mr. Choe is widely considered one of Mr. Kim’s closest aides. He visited Beijing in May of last year and met with President Xi Jinping of China.

Mr. Choe’s trip to Moscow comes as North Korea is relying on its old Cold War allies, China and Russia, to veto any United Nations move to bring Mr. Kim before the International Criminal Court on accusations that his country violated human rights.

In February, a United Nations panel submitted a report accusing the North Korean government of systematic torture, killings and starvation and said top leaders could be held accountable for crimes against humanity. The General Assembly is expected to vote on a resolution condemning North Korea’s human rights abuses later this year, but only the Security Council, where Russia and China wield veto power, can refer the matter to the international court. China, North Korea’s main ally, has already indicated it will probably block such a move.

The North Korean government has recently tried to improve its relations with Moscow as a possible counterbalance to China. Beijing has been under international pressure to use its economic influence to discourage the North from conducting nuclear and missile tests and engaging in other acts seen by the West as provocations. Years of sanctions have left North Korea increasingly reliant on trade with China, and leaders in Pyongyang, the capital, have grown uncomfortable with that economic dependence, and the leverage it gives Beijing, analysts said.

For its part, Russia has tried to coax North Korea into cooperating with its economic expansion in the Far East.