SEOUL, South Korea (CNN) -- U.S. nuclear envoy Christopher Hill arrived in North Korea Wednesday for talks aimed at saving a disarmament deal with the reclusive communist nation, the U.S. Embassy said.
"So I would say we are in a very difficult and very tough phase of negotiation," Hill said ahead of his meetings with North Korean officials. "And again, the full importance of that, I think, will be seen when we determine which way we are finally heading on this."
Hill's visit came at the invitation of North Korean officials and was part of a multi-capital trip that also includes South Korea, China and Japan.
"The North Koreans invited Chris Hill to come, so we hope that there is some effort to address the verification protocol, because that's what we need," U.S. Secretary of State Condoleezza Rice told reporters Monday.
"We need to move forward on the verification protocol. I think everybody is in agreement in the six parties, and -- or among the five parties, and so we'll look to see what they have to say." Watch what's proving to be the sticking point »
State Department officials said Hill was bringing proposals on how North Korea could deliver the verification to China first, instead of sharing it with the other five parties all at once, as was originally planned.
Spokesman Sean McCormack said Hill would be discussing "choreography," but that Hill "wasn't bringing with him any new substance, in terms of proposals"
Six-party talks involving North Korea and five other nations came to an agreement on its disablement of its Yongbyon nuclear reactor and reprocessing facilities that produced plutonium for nuclear weapons.
But in recent weeks, after the United States insisted on measures to verify information North Korea has provided, Pyongyang has taken steps that could reverse course and put the facilities back on line.
"I would say what they [North Korea] have been doing obviously goes counter to the spirit of what we've been trying to accomplish because all of the shut down and disablement was for the purpose of abandonment," Hill said. "It was not for the purpose of any efforts at the reversal."
North Korea said the United States has not followed through on its promise to take the country off the U.S. list of countries that sponsor terrorism. The United States says it can't do that without the verification.
The impasse has come amidst unconfirmed reports that North Korean leader Kim Jong Il may be seriously ill. Kim has been absent from numerous events he would normally attend, leaving many wondering who is in charge.
The United States and its allies in the six-party talks insisted North Korea must provide a package of information on how to verify its earlier statements, some 19,000 pages of documents, about the scope of its entire nuclear program.
The North Koreans claim the United States' demands are too intrusive.
CNN's Elise Labott contributed to this report.