President Donald Trump and South Korean President Moon Jae-in have signed the first major agreement of Trump's trade agenda.

The leaders signed an update to an existing U.S.-South Korea free-trade agreement Monday in New York. Both leaders are attending an annual U.N. gathering.

Trump calls it a "very big deal" and says the new agreement makes significant improvements to reduce the trade deficit between the countries and create new opportunities to export American products to South Korea. He says U.S. automobiles, pharmaceuticals and agricultural products will gain better access to Korean markets.

Moon says companies from both countries will be able to do business under more stable conditions. The South Korean leader also said he hopes the revised agreement with the U.S. will help solidify their cooperation in other areas.

WATCH: S. Korea trade deal won't benefit US automakers much