SEOUL, South Korea (AP) — South Korea said Tuesday it will investigate emission levels of Volkswagen diesel vehicles after the world's top-selling automaker admitted cheating U.S. tests.

Park Pan-kyu, a deputy director at South Korea's environment ministry, said that four models — Golf, Jetta, Beetle and Audi A3 — are subject to the probe, which is expected to end in November. About 6,000 vehicles made in 2014 and 2015 were sold under those nameplates in South Korea.

Volkswagen AG admitted that it rigged U.S. tests so it would appear that its diesel-powered cars were emitting fewer nitrogen oxides, which can contribute to ozone buildup and respiratory illness.

Park said Volkswagen could be fined up to 4 billion won ($3.4 million) and required to recall the vehicles if wrongdoing is found.

"Volkswagen Korean office says that South Korean models are different from the U.S. models but we'll have to test," Park said. "We think they could be similar."

The German automaker's Korean office declined to comment.

Some $15 billion was wiped from Volkswagen's market value after the U.S. Environmental Protection Agency announced the violations on Friday.

The automaker faces up to $18 billion in penalties in the U.S. alone.

Volkswagen overtook Japan's Toyota Motor Corp. to become the world's top-selling automaker in the first half of the year.