South Korea says 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 Tuesday that four models — Golf, Jetta, Beetle and Audi A3 — are subject to the probe, expected to end in November. About 6,000 vehicles made in 2014 and 2015 were sold under those nameplates in South Korea.

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

Volkswagen AG admits 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.

Some $15 billion was wiped from the automaker's market value after the revelation.