SEOUL (AFP) - A scandal over educational privilege in South Korea that threatened to derail the new justice minister's appointment has spread to engulf the opposition's parliamentary leader, whose son is a student at Yale University.

The world's 11th largest economy is an intensely competitive society, where teenage students are under tremendous pressure to win admission into elite universities.

Success can lead to lifelong advantages in employment, society and even marriage, and any hint of manipulation of the process by wealthy or influential parents outrages ordinary South Koreans.

Prosecutors in Seoul said on Wednesday (Sept 18) that they had opened a probe into allegations that Ms Na Kyung-won, the parliamentary floor leader of the opposition Liberty Korea party, pressured a Seoul National University professor to accept her son as an intern.

The teenager was later named the lead author of a medical paper that won him first prize in a US scientific competition - Research on the Feasibility of Cardiac Output Estimation Using Photoplethysmogram and Ballistocardiogram - and he subsequently secured a place at Yale to study chemistry.

But his supervisor Yoon Hyung-jin told broadcaster KBS that the paper was "beyond the level that a high schooler could have comprehended".

"It's clear he had not understood what he was doing," he said. "But we gave him ideas."

The allegations directly parallel the accusations against Justice Minister Cho Kuk, who barely survived confirmation scrutiny this month when it was revealed his daughter was named lead author of a medical paper during her high school years, helped by her family connections.

Ms Na - who was a classmate of Mr Cho at Seoul National University, where they studied law in the early 1980s - had herself been one of the new justice minister's fiercest critics, accusing him of ensuring his daughter's resume was "riddled with lies".

Ms Na maintains her son is solely responsible for the paper and has denied foul play.

Score-settling is ingrained in the country's winner-takes-all political system, with every one of the country's living former presidents either currently in prison or convicted of crimes after leaving office.