Korea's trade surplus with the U.S. expanded over the first seven months of this year, and especially after their bilateral free trade agreement went into effect in March.

The U.S. Department of Commerce said on Tuesday that the country's trade deficit with Korea increased by more than 16 percent from January to July compared to the same period one year earlier.

The July edition of the department's International Trade in Goods and Services report shows that the U.S. imported US$34.9 billion worth of goods from Korea and exported $25.7 billion, creating a deficit of $9.1 billion.

Automobiles and car parts played the biggest role in the U.S. logging an auto-related trade deficit of nearly $11 billion with Korea this year.