Earlier in the talks the U.S. had pressed South Korea to lift restrictions on imports derived from cattle older than 30 months, but Yeo helped defuse that by showing the Americans a photo of massive protests that occurred years ago over concerns about mad cow disease.

President Donald Trump said he had reached a trade deal with South Korea that would impose a 15% tariff on its exports to the US and see Seoul agree to $350 billion in US investments.

"I think it's the biggest deal ever made," Trump said of the new agreement, which will reduce the bloc's tariff rate to 15 percent.