SEOUL (Reuters) - South Korea will launch a special probe into violations of the free trade pact with the United States regarding country of origin markings, the Korea Customs Service (KCS) said on Tuesday, ahead of U.S. President Donald Trump's tariffs.

South Korea is among 20 countries worldwide, and one of only three in the Asia-Pacific region, that has a free trade agreement with the United States. Under this pact, nearly all tariffs are eliminated for goods traded between the two countries.

The KCS said it would investigate products exported to the U.S. for violations in marking the country of origin.

Authorities will take firm action against companies knowingly disguising foreign goods as South Korean products to protect domestic companies and the authenticity of South Korean exports, the KCS said.

"We are taking preemptive action to protect domestic companies as there are concerns from earlier experience during the first Trump presidency that U.S. verifications might become stricter after imposing higher tariffs," a KCS spokesperson said.

Products at high risk of false markings, such as those subject to U.S. anti-dumping tariffs or closely watched by U.S. customs authorities, will be scrutinised, the KCS added.

The Trump administration said it would prepare reciprocal tariffs against its major trading partners by April 2, after imposing steep tariffs on imports from China as well as those from Canada and Mexico that do not comply with their free trade pact.