Assistant Secretary of State Christopher Hill, right, is surrounded by reporters upon arrival at Foreign Ministry in Seoul, 03 Oct 2008

U.S. nuclear envoy Christopher Hill is expected to leave North Korea Friday after spending the last three days attempting to revive a faltering deal for dismantling North Korea's nuclear program. 

Hill crossed the demilitarized border Wednesday to hold talks in Pyongyang with his North Korean counterpart Kim Kye Kwan.  He was due to return to Seoul Thursday, but decided to extend his trip.

The assistant U.S. secretary of state was expected to propose ways to adjust the sequence of steps North Korea must take to verify its nuclear program.

State Department spokesman Sean McCormack says Hill did not make substantive concessions to North Korea, but he would discuss changes in how the agreement is "choreographed."

U.S. officials say Hill was expected to propose that North Korea be removed from the terrorism list provisionally, if it gives a verification plan to China, its closest ally.

North Korea accuses Washington of reneging on a commitment to remove Pyongyang from the U.S. list of state sponsors of terrorism after North Korea made a declaration of its nuclear holdings in June.

The United States says removing North Korea from the list depends on it providing a plan to verify the nuclear declaration.

Last year, North Korea agreed to end its nuclear program in return for energy aid and diplomatic benefits from the United States, South Korea, Japan, Russia, and China.  However, in recent weeks, North Korea reversed the process of dismantling its nuclear facilities.

The difficulties in the disarmament process came amid reports that North Korean Leader Kim Jong Il suffered a stroke in August, possibly disrupting the decision-making process in Pyongyang.

Wednesday, South Korea's Yonhap news agency quoted a government source as saying there are signs of renewed activity at an underground test site where North Korea detonated an nuclear device in 2006.

Some information for this report was provided by AFP and AP.