Ri Gun, a deputy negotiator in stalled talks over the hermit state's nuclear program, arrived Friday with his delegation, an official at North Korea's United Nations mission told AFP.

The visit, which came after the United States took the unusual step of granting a visa to the North Korean officials, is expected to last several days. The delegation was to attend several conferences in the United States.

State Department spokesman Ian Kelly said late Friday that no decision had been taken on who would meet Ri. But he did not rule out the prospect of talks between the senior negotiator and Sung Kim, the US special envoy for North Korean disarmament talks.

"I wouldn't exclude that. I don't have anything to announce about that, but I certainly wouldn't exclude it," Kelly said.

Ri is expected at the University of California in San Diego on Monday for closed-door informal talks on the nuclear standoff, according to the event's director, Susan Shirk.

The delegation was also scheduled to attend a seminar in New York hosted by the National Committee on American Foreign Policy and the Korea Society.

Kelly said no decision had yet been made on which US official would attend the San Diego meeting, organized by the Institute on Global Conflict and Cooperation.

On Thursday, the institute released a study urging the United States to scrap its policy of isolating North Korea and embrace economic engagement in order to curb the reclusive communist state's provocative behavior.

The recommendations made in the study by Shirk and other experts included dropping objections to Pyongyang's entry into global financial institutions like the International Monetary Fund.

The study flew in the face of the approach undertaken by President Barack Obama, who has pushed to toughen sanctions after Pyongyang's string of incitements, including a nuclear test and missile launches.

Ri's rare visit fueled speculation that North Korea is preparing to return to talks about its nuclear weapons program with South Korea, Japan, China, Russia and the United States.

US Assistant Secretary of State for East Asian and Pacific Affairs Kurt Campbell said Monday that Washington was ready to meet one-on-one with Pyongyang but only if it "rapidly" leads to full-fledged denuclearization talks in the six-nation forum.

On October 6, North Korean leader Kim Jong-Il told Chinese envoys the North was willing to return to six-way talks, but insisted it first negotiate directly with the United States to repair "hostile relations."

Campbell said the United States "would be prepared for, in the right circumstances at some point, some initial interaction" with North Korea "that would lead rapidly to a six-party framework."

North Korea has long sought to meet exclusively with the United States and gain recognition as a nuclear weapons state.

The possible diplomatic overtures come after senior US officials fired tough words at Pyongyang.

On Thursday, US Defense Secretary Robert Gates, visiting South Korea, labeled North Korea a grave threat to international peace and promised to keep Washington's allies in East Asia under its nuclear umbrella.

The United States has 28,500 troops in South Korea, bolstering that nation's 655,000-strong armed forces against the North's 1.2 million troops.

South Korean Defense Minister Kim Tae-Young said the North's policy had not changed despite recent diplomatic overtures.

Secretary of State Hillary Clinton has warned that the United States will never have "normal, sanctions-free relations" with a nuclear-armed North Korea and demanded Pyongyang's full nuclear disarmament.

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