"We will kickstart our coal phase-out," said Seoul's Climate Minister Kim Sung-whan, announcing South Korea's decision to join the Powering Past Coal Alliance (PPCA) of governments and organisations pushing to eliminate unabated coal as a power source.

The pledge will "help the Alliance advance the coal transition worldwide", added Kim, who is attending the United Nations' annual COP climate summit in Brazil.

Unabated refers to coal burned without any measures to reduce its emissions, such as carbon capture or storage.

The pledge does not give a date for an end to all South Korea's use of unabated coal, but represents the first official government commitment to stop building new unabated coal plants and to phase out existing ones.

"Out of 61 existing coal power plants, 40 coal power plants are confirmed to phase out by 2040," the PPCA said in a statement.

The remaining 21 plants will have their closure date "determined based on economic and environmental feasibility", with a detailed roadmap to be finalised in 2026, the group added.

Asia's fourth-largest economy currently operates the world's seventh-largest coal fleet and is the fourth-largest coal importer, according to the PPCA.

The pledge demonstrates South Korea's "commitment to accelerating a just and clean energy transition", Kim said.

The transition will "create thousands of jobs in the industries of the future," the minister added.

South Korea has already begun cutting its dependence on coal, with its share of electricity generation falling to 30.5 percent last year from 46.3 percent in 2009, according to energy think tank Ember.

The new commitment builds on Seoul's 2020 pledge to reach carbon neutrality by 2050.

As part of that target, the government aims to reduce greenhouse gas emissions by 53-61 percent from 2018 levels by 2035, in line with global efforts to limit warming to 1.5C.

Dozens of countries worldwide have pledged to phase out unabated coal.

South Korea is only the second government in Asia to join the PPCA, after Singapore.