WASHINGTON  (Yonhap News) -- South Korean President Lee Myung-bak said his denuclearization push against North Korea is yielding progress, reaffirming his long-standing stance that Seoul won't provide Pyongyang with any large-scale aid unless Pyongyang disarms.

"There are some real changes we are detecting," Lee said in an interview with the Washington Post published online on Tuesday. "In the past, if we had dialogue between the two Koreas, it was never about nuclear weapons. The discussion was only about when and how much aid we would give."

Since taking office in early 2008, Lee has linked any massive aid to Pyongyang to progress in international efforts to end its nuclear programs. That stance angered Pyongyang, souring relations between the two countries and leading the regime to stage a series of provocations in an attempt to force a change in Lee's hard-line stance.

In the interview held in Seoul, Lee made clear that his government won't provide any aid to the impoverished neighbor unless Pyongyang denuclearizes.

The United States has been a big supporter of Lee's stance as it agrees with Lee's point that improvement in inter-Korean relations is a precondition for better ties between Seoul and Washington.

That U.S. stance effectively forced North Korea to agree to bilateral nuclear talks with South Korea, a concession that breaks away from the communist nation's usual reluctance to discuss the nuclear standoff with Seoul.

Two rounds of inter-Korean nuclear talks have been held, first in July and the latest meeting last month. Washington is also expected to hold its second round of talks with the North possibly later this month.

Lee arrived in Washington earlier Tuesday for a five-day state visit centering on a free trade agreement between the two countries. Congress is expected to approve the landmark agreement on Wednesday, a day before Lee's summit talks with Obama.

Lee touted the trade deal as an "economic alliance," saying in the interview that the pact would also strengthen the overall relationship between the two countries.

On Thursday, Lee is scheduled to address a joint session of Congress, a rare event organized to mark the deal's ratification. Lee will be the first South Korean leader to speak at a joint Congressional session in 13 years after a 1998 speech by late former President Kim Dae-jung.

Lee and Obama also plan to travel together to Detroit, the heart of the U.S. auto industry, on Friday, a symbolic move apparently aimed at promoting the benefits of the trade accord amid American automakers' concerns that it could hurt their interests.

On his way home, Lee plans to spend a night in Chicago, Obama's political hometown, for a dinner meeting with business leaders of the two countries that will be hosted by Chicago Mayor Rahm Emanuel, who had served as Obama's chief of staff. The trade deal will be a key topic there as well, officials said.