A U.S. envoy says she admires the "vision and scope" of a South Korean-funded industrial zone in North Korea.   But after a daylong tour of the zone, the envoy said the project's ambitious goals are only likely to be realized after North Korea finally decides to end its nuclear weapons threat.

South Korean workers clean on the railway tracks, which the two Koreas hope to reconnect as a part of an agreement

Kathleen Stephens, the senior U.S. assistant secretary of State for East Asian Affairs, visited the Kaesong inter-Korean industrial zone Friday.

South Korea funds the zone, which lies in North Korea. Seoul considers the zone a triumph for its agenda of economic cooperation and engagement with communist North Korea.

Stephens says Friday's tour was a learning experience for her.

"I think I have a sense of what this means to Koreans, and of how their aspirations are so high for it," said Ms. Stephens.  "Of the scope of the project as they envision it.  I don't think I'd really appreciated that before."

About 6,000 North Koreans, handpicked by Pyongyang, work in the zone for more than 10 South Korean companies. South Korean authorities say they hope to expand the zone to give more than half a million North Koreans employment in the global economy.

South Korea says the North Korean workers receive about $50 a month, paid through North Korean authorities. However, U.S. North Korea Human Rights Envoy Jay Lefkowitz drew fire from South Korean officials earlier this year when he cautioned that "little is known" about actual working conditions there.

Other critics of North Korea have said it is not clear how much of the salary actually goes to the workers.

Stephens says South Korean guides assured her that efforts are underway to make Kaesong operations conform to global labor standards.

"I get the impression that there are still parts of this that are going to be worked out, to be more transparent both to the workers and to the outside world," she added.

Stephens cautions, however, that North Korea's nuclear weapons programs pose a serious obstacle to the Kaesong zone's plans for growth.

"We're still waiting to see if that strategic decision has been made by the DPRK, that they really do want to engage in this process, and which would only underpin and galvanize, if you like, the vision of what Kaesong could be that I heard today," She noted.

North Korea says it is building more nuclear weapons, despite international pledges it signed not to do so.  The United States, Russia, China, Japan, and South Korea have tried for three years to persuade Pyongyang to disarm in exchange for a package of economic and diplomatic incentives.

South Korean President Roh Moo-hyun has promised unconditional continuation of economic support for the North. Washington insists the nuclear issue must be resolved before it increases aid to Pyongyang.