South Korea's Prime Minister Lee Nak-yon on Tuesday voiced optimism for three-way economic cooperation involving the two Koreas and Russia amid Seoul's stepped-up diplomacy to facilitate Pyongyang's denuclearization.

"On Sept. 18, there will be a third inter-Korean summit.

High-level talks between the North and the United States are also expected to resume," Lee said during his speech at the South Korea-Russia Business Dialogue in the Russian far eastern port city of Vladivostok.

"There will be a new avenue opening for three-way cooperation among South and North Korea and Russia," he added.

Lee was in Vladivostok to attend the Eastern Economic Forum that Russian President Vladimir Putin has hosted in the city every year since 2015.

South Korean President Moon Jae-in and North Korean leader Kim Jong-un are set to hold their third summit in Pyongyang from Tuesday through Thursday next week, with the agenda likely to focus on Pyongyang's nuclear disarmament.

The decadeslong nuclear issue has long been a major hurdle for economic exchanges and cooperation between the two Koreas and among the two Koreas and Russia.

Touching on the Seoul-Moscow relationship, the prime minister stressed four things: strengthening cooperation in the development of Russia's far eastern region, the manufacturing sector, future industries and three-way cooperation that includes the North.

During the event, Korea International Trade Association chief Kim Young-joo pointed out that Russia's far east has been emerging as an attractive investment destination.

"(We) are looking to find the possibility of future development through cooperation with Russia in this region replete with potential," he said.

(Yonhap)