US President Donald Trump welcomed Seoul's planned purchase of US military equipment Tuesday, saying it will help narrow his country's trade deficit with South Korea.

The remarks came at the start of an expanded summit with President Moon Jae-in, following their one-to-one talks.

Trump said he had learned through his representatives that the "amount of equipment and things you will be ordering from the United States will substantially increase, and therefore bringing the trade deficit down, which is very important to our people."

"We have trade deficits with numerous countries and we don't want trade deficits, so we appreciate that very much," he said, according to a video feed of the summit broadcast live and later posted by the presidential office Cheong Wa Dae.

Moon expressed hope that Trump's visit will give a momentum to resolve the North Korean nuclear standoff.

"I wish you will help give assurances to our people on a peaceful resolution of the North Korean nuclear issue during your visit here, while at the same time sending a strong message to the North," the president said.

Trump arrived here earlier in the day, becoming the first US president in 25 years to make a state visit to the country.

The Moon-Trump talks marked the third of their kind since the two came into office earlier in the year. Their two previous meetings were held in Washington and New York. (Yonhap)