South Korea's envoy to six-nation negotiations on North Korea's nuclear program is heading to the United States as diplomatic efforts to end a three-year freeze in the talks intensify.

South Korea's Yonhap news agency says Wi Sung-lac will arrive in Washington Wednesday to hold two days of talks with Stephen Bosworth, Washington's special envoy to North Korea, and Clifford Hart, who is expected to be named the chief U.S. envoy to the six-nation talks.

The United States, Russia, China, Japan and South Korea have been negotiating with impoverished North Korea for eight years to get it to give up its nuclear weapons programs in exchange for food, energy and aid. The talks have been frozen since Pyongyang quit the negotiations in 2008, and later resumed testing of nuclear weapons and ballistic missiles.

North Korea has been seeking a resumption of the talks in recent months but South Korea and the United States have insisted that it first follow through on past promises to disarm.

During talks with Russian President Dmitry Medvedev last month, North Korean leader Kim Jong Il expressed a willingness to impose a moratorium on his country's nuclear program if the talks resume.

In July, nuclear envoys from the rival Koreas held rare talks on the sidelines of the ASEAN security conference in Bali, Indonesia. That was followed by a round of talks between North Korean and U.S. diplomats in New York.