South Korea's Foreign Minister Ban Ki Moon is in Washington for discussions with U.S. officials on North Korea's nuclear program. Both countries are represented in six-nation talks on the North Korean nuclear crisis. The talks are set to resume in Beijing at the end of this month.

Speaking on CNN's "Late Edition," South Korean Foreign Minister Ban Ki-Moon sounded upbeat about the current round of six-party talks on North Korea's nuclear program.

"I think during last round of our six party talks, we have entered into a stage of real and substantive negotiations," he said. "This is what we have been doing and, with close consultations between Korea and the United States, also with other related parties, I think we are more or less optimistic that we will be able to result in a substantive resolution of nuclear weapons program this time."

The talks also include North Korea, China, Japan and Russia.

Foreign Minister Ban could not confirm Japanese news reports that North Korea had restarted a nuclear reactor in July, before the latest round of talks resumed. But he said South Korea is closely monitoring the situation and he urged all countries not to take actions that could aggravate the ongoing talks.

One outstanding issue is North Korea's insistence on retaining the right to use nuclear energy for peaceful purposes, a position the United States has rejected. The South Korean official said Seoul does not have what he described as "much difference" with Washington. But he said if Pyongyang returns to the Nuclear Non-Proliferation Treaty and complies with International Atomic Energy Agency safeguards, his country is willing to discuss North Korea's peaceful use of nuclear energy for medical or industrial purposes.

"We are of the view that once North Korea dismantles all nuclear weapons and programs, and returns to NPT and comes into full compliance with the full scope of IAEA safeguards, then trust will be restored and the door for peaceful use of nuclear energy should be open," added Mr. Ban.

The peaceful use of nuclear energy is not the only outstanding issue, though, according to U.S. negotiator Christopher Hill, who spoke in Washington last week at the Asia Society.

"We do have, still, some serious outstanding differences. I know there's been a lot of focus, especially in the U.S. press, about the issue of so-called peaceful use, that is, the idea that North Korea should retain the right to having, to developing nuclear energy," said Mr. Hill. "I would caution people on the idea that this is the only difference, because there are a number of other differences that we need to address."

Ambassador Hill said a frank and businesslike exchange of views during the six-party talks, on North Korea's highly-enriched uranium program, was ultimately inconclusive. "I cannot say we resolved that issue except to make clear that it's an important issue that needs to be resolved," he added.

He declined to specify other sticking points, saying making them public would be harmful to the ongoing negotiations, which are set to resume next week. Ambassador Hill compared the six-party talks to pushing a large rock up a hill, saying it would be too much to bear if, after the three-week recess, the rock came crashing back down. So, he concluded, he is, in his words, "very interested in holding things where they are."