The United States has offered to hold trilateral high-level talks with South Korea and Japan to resolve a growing trade spat between the Asian nations, but Tokyo has yet to respond, a top South Korean presidential official said Thursday.

Kim Hyun-chong, deputy chief of Cheong Wa Dae's National Security Office, said Seoul and Washington are eager to have the meeting to discuss Japan's recent export curb measures against South Korea.

"We would like to seek a constructive solution, but the Japanese side still hasn't responded," Kim told reporters outside his hotel in Washington, where he has been meeting with White House officials and members of Congress to raise awareness of South Korea's position in the dispute.

"A high-level American official will be traveling to Asia, so the US wanted to use the opportunity to have a three-way meeting, but while South Korea and the US are very eager, the Japanese side appears to be a bit passive," he later elaborated before heading to a meeting with US Trade Representative Robert Lighthizer.

When asked, he declined to say whether the US official is David Stilwell, the top US diplomat for East Asia who is currently in Japan and due to visit Seoul next Wednesday.

The assistant secretary of state for East Asian and Pacific affairs is on his first tour of the region since taking office last month. Expectations are that he will try to bridge the divide between the two US allies.

Last week, Japan toughened restrictions on exports of key materials used in semiconductors and displays in apparent retaliation for a South Korean court ruling that ordered Japanese firms to compensate South Korean victims of forced labor during Tokyo's 1910-45 colonial rule of the Korean Peninsula.

South Korea has raised the case at the World Trade Organization and sought to explain the move's damaging effects on not only the South Korean economy but also the US and world economies.

The US State Department expressed its commitment to strengthening ties with both South Korea and Japan and among the three countries.

"I would say that Japan and South Korea are of course not only friends, they're allies," department spokeswoman Morgan Ortagus said during a press briefing. "The United States and of course here at the State Department, we're going to do everything we can to pursue ways to strengthen our relationships between and amongst all three countries, both publicly and behind the scenes."

Kim told reporters after meeting Lighthizer that the US official offered to inform the South if the US finds a way to help resolve the dispute.

On Wednesday, Kim held talks with acting White House chief of staff Mick Mulvaney, as well as with members of the Senate.

Mulvaney expressed hope that the two US allies will be able to settle the dispute in a constructive manner, according to Kim.

The senators he met also voiced similar opinions, he said.

On Friday, Kim is scheduled for talks with Deputy National Security Adviser Charles Kupperman.

He said the two will discuss a wide range of issues, including negotiations over North Korea's nuclear weapons program and what the US aims to achieve as the end state.

The US and North Korea are expected to resume talks in the middle of this month in line with an agreement between US President Donald Trump and North Korean leader Kim Jong-un during their meeting at the inter-Korean border on June 30.

"I can't say for certain whether they will be held next week or the week after," the South Korean official said. "We're still waiting for a response, so I think we'll have to wait and see."

As part of a governmentwide effort to win US backing, Kim Hee-sang, director-general for bilateral economic affairs at Seoul's foreign ministry, also held meetings with State Department officials in Washington.

"We had sufficient discussions on the problems that will be caused by Japan's strengthening of export controls, and I think it was an opportunity for the US to fully understand that," he told reporters. "The US side is fully aware of the issue and understands the seriousness of it."

Kim met with Roland de Marcellus, acting deputy assistant secretary of state for international finance and development, and Marc Knapper, deputy assistant secretary of state for Korea and Japan.

South Korean Trade Minister Yoo Myung-hee is expected to visit the US next week to continue discussions on the issue. (Yonhap)