Macri said his country will continue to support efforts to peacefully resolve the North Korean nuclear issue.
"Peace on the Korean Peninsula will solidify and both the South and North will prosper together as our railways link as one in the future", Unification Minister Cho Myoung-gyon said in a congratulatory speech.
A South Korean train with a sign reading "Seoul to Sinuiju" crossed into the North, Friday, for a long-stalled joint inspection of railway sections there.
Secretary of State Mike Pompeo was due to meet with a top North Korean official in early November, but the meeting was abruptly put off, with North Korea insisting that the United States ease sanctions.
The six-carriage train carried 28 South Koreans, including railway engineers and other personnel, as well as 55 tonnes of fuel and an electricity generator.
The South's Unification Ministry has earmarked some 63.4 billion won (S$77 million) for next year on the assumption that it will take five years to fix and improve the two railway routes in the North.
It is also the first time for a South Korean train to run from Mount Kumgang to Tumen River since the peninsula was divided following the 1950-53 Korean War.
At Panmun Station across the border, a North Korean engine took over to take them further north.
Cho also promised to maintain close consultation "with related nations" - in other words, the United States - so that the project proceeds with worldwide support.
The announcement of the apparent defection comes a day after the two Koreas completed the destruction of 20 guard posts (GPs) in the demilitarized zone (DMZ).
The plan to modernize North Korea's outdated railways and roads came from the historic meeting between the two country's leaders in April, in which North Korea's Kim Jong-un asked for help with updating the country's "embarrassing" railway network.
The joint railway surveys were on hold before the U.N. Security Council on Saturday granted an exemption to sanctions that allowed them to proceed.
At Kaesong, South Korea's locomotive was swapped with North Korea's, and three North Korean cars which Seoul's Unification Ministry did not immediately specify were attached to the six South Korean cars.
Twenty-eight South Korean officials including people from the unification, and land, infrastructure and transport ministries will inspect the 400-kilometer section from Gaeseong to Sinuiju through December 5.