President Moon Jae-in was speaking to Russian news media before a three-day visit to Moscow starting Thursday, with the presidential Blue House releasing the transcript.

Russia and South Korea agreed in 2008 to lay gas pipelines through the North to bring Russian natural gas to the South. But the project failed to take off due to tensions over the North's nuclear weapons programme.

Restoring inter-Korean railroads and linking them to trans-Siberian railways would also enable overland transport from trade-dependent South Korea to Europe, Moon added.

"This will bring huge economic benefits to the South and the North as well as Russia," he said.

At the unprecedented summit between the North and the US in Singapore last week, US President Donald Trump showed Pyongyang's Kim Jong Un a video showing the North transformed by economic growth.

The summit, Moon said, had "succeeded beyond all expectations", although some analysts said little of substance was agreed.

In a joint statement afterwards the North committed to "work toward complete denuclearisation of the Korean peninsula", without making an explicit commitment to give up its weapons.

The two rivals also agreed to establish new ties and work to build a "lasting and stable peace regime" on the Korean peninsula.

But Moon said that "Chairman Kim has expressed his willingness to give up his nuclear arsenal and focus on economic build-up should the North be guaranteed safety".

At earlier summits of his own with Kim, Moon added, the North Korean "turned out to be frank and straightforward and despite his age, maintained his composure" throughout their long talks.

South Korea must import the vast bulk of its oil and gas. But despite their geographical proximity Russia is only its sixth-biggest supplier, providing just 5.5 percent of total needs.