Incheon Mayor Song Young-gil left for Moscow on Wednesday for a five-day visit, during which he is expected to meet with Russian President Vladimir Putin.
The visit comes at the invitation of Putin, and Song's meeting with the Russian president is scheduled for Friday, city officials said.
They said Putin gave no clear reason for inviting the mayor.
Incheon city officials said, however, that Putin is expected to award a state medal to Song to recognize the mayor's role in promoting ties between the nations.
When he meets with Putin, Song may ask him to help convince North Korea to drop its plan to conduct a third nuclear test, the city officials said.
Tension has spiked on the Korean Peninsula as North Korea has threatened to carry out a nuclear test in retaliation for a U.N. Security Council resolution that punished Pyongyang for its December rocket launch.
Song's trip has raised speculation that he might play a role as an unofficial envoy for South Korean President-elect Park Geun-hye, but the mayor denied it.
"It is a schedule between the Russian government and the Incheon city and our government did not give any role to me," Song told reporters before leaving Seoul.