Unveiling a report on South Korea's energy policies, the IEA backed the country's nuclear programme, but said more needed to be done to restore faith in a sector also facing greater global scrutiny after last year's Fukushima nuclear disaster in Japan.
"Given the growing demand for energy and Korea's lack of indigenous energy resources, this is a logical policy," Maria van der Hoeven, the IEA's executive director, said in a statement.
"Nonetheless, recent incidents at Korean nuclear facilities should serve as a timely reminder to the government that the nuclear regulatory authority must maintain an enhanced profile, be well-resourced and able to take independent decisions."
Asia's fourth-largest economy lacks its own energy resources and depends heavily on oil and gas imports while 23 nuclear reactors usually supply a third of its power. The country plans to add 11 more by 2024.
But the nuclear sector has suffered a big blow after an investigation into fake safety documents for parts led to two reactors being shut and after an extended shutdown of another reactor where microscopic cracks were found.
The South Korean government has been criticised for a lack of transparency over safety in its nuclear programme and for the dual supervisory and promotion roles of its regulators.
The country's public is traditionally seen as pro-nuclear, although an opposition lawmaker has pressed the government to resume publishing polls on nuclear safety after a loss of public confidence in the sector in the wake of Fukushima.
There is a lot at stake for South Korea, which aims to export 80 nuclear reactors by 2030, expected to be worth up to $300 billion, according to government plans. A $20 billion deal with the United Arab Emirates has already been signed.
Highlighting the vulnerability of its energy sector, South Korea has warned it may have to bring in rolling power blackouts during the harsh Korean winter due to a lack of nuclear power.
Six reactors are currently offline, with one restarting earlier this week, according to government data.
Ms van der Hoeven says the country needs to increase competition in its power and gas markets.
"The lack of a clear, long-term vision for electricity and natural gas markets is one of the greatest energy-policy challenges facing the Korean government," she said.
"The IEA strongly urges the Korean government to establish a framework that allows the development of effective competition in the electricity and natural gas markets."