"We hope it means that the North Korean leadership is making a strategic decision to denuclearize and join the international community," Vershbow told a security forum in the South Korean capital.
US officials have said the visit to North Korea is a hopeful sign that, almost a year after North Korean first tested a nuclear weapon, it is serious about permanently shutting down its nuclear programme.
The visit is taking place under a six-nation deal agreed in February in Beijing, under which North Korea agreed to declare and disarm its nuclear weapons programmes in return for aid, security guarantees and major diplomatic benefits.
The six-nation talks bring together envoys from North and South Korea, Japan, China, Russia and the US.
In Washington US State Department spokesman Sean McCormack said the team visiting North Korea had been allowed to see everything they wanted to see.
McCormack said that while Friday's talks in North Korean would begin to lay down plans for dismantling Yongbyon, any agreement on the practicalities of how to dismantle Yongbyon would be reached within the six-party talks.
"It's really to talk a little bit about some of their initial impressions about what they saw and how you might go about actually disabling the reactor," he said.
"Any sort of agreement would happen within the six-party context."
In July North Korea shut down the Yongbyon plant, home to its only operating reactor, in return for 50,000 tonnes of fuel oil.
The next step is to permanently disable all it nuclear facilities by encasing them in concrete or some other method which the experts will advise on.
If the North declares and disables all its plants it will receive another 950,000 tonnes of fuel oil or equivalent energy aid.