Five International Atomic Energy Agency (IAEA) investigators left the country after a third round of investigations which began last Tuesday, the Korea Atomic Energy Research Institute said.

South Korea has been under IAEA scrutiny since its revelation in early September that its scientists secretly enriched a tiny amount of plutonium in 1982 and of uranium in 2000.

Seoul officials said the latest inspection was the last before UN inspectors present a report to an IAEA board meeting on November 25. The board will decide whether to refer the case to the UN Security Council, which can impose sanctions on nuclear arms proliferators.

Seoul has said the nuclear experiments, which were conducted without the government's knowledge and thus undeclared, were scientific research not linked to any weapons programs.

The IAEA has sent inspectors to South Korea three times to inspect nuclear facilities, interview scientists and take samples.

North Korea, citing concern about Seoul's secret nuclear experiments and "hostile" US policy, boycotted a planned new round of six-nation talks aimed at ending the communist state's atomic weapons drive.

South Korea operates 19 nuclear power plants producing 40 percent of its energy needs.

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