Tokyo ? A team of U.S. experts will begin disabling North Korea’s nuclear facilities on Monday, the U.S. envoy said today, marking a major concrete step by the communist country in scaling back its atomic program.

Top U.S. envoy Christopher Hill said in an interview that aired by public broadcaster NHK that the team would travel Sunday to North Korea’s main nuclear complex at Yongbyon, north of the capital, Pyongyang.

Hill said the group, which arrived in Pyongyang on Thursday, would then start disabling the country’s sole functioning reactor there and two other facilities on Monday.

“By Monday morning, they will begin dismantlement,” Hill said. “It’s a very big day because it’s the first time it’s actually going to start dismantling its nuclear program,” he said.

The North already shut down the reactor in July, and promised to disable it by year’s end in exchange for energy aid and political concessions from other members of talks on its nuclear program: the U.S., China, Japan, South Korea and Russia.

Disabling the reactor would mark a milestone in efforts to convince the North to scale back its nuclear program. The country conducted its first-ever nuclear test in October of last year.

The North could still restart the reactor even after disablement, though Hill has said that process would take at least a year. The U.S. and other countries in the nuclear talks demand that Pyongyang completely dismantle its nuclear weapons program.

Hill said Friday that the United States was working with North Korean officials on the issue of the communist country’s designation as a state sponsor of terrorism.

He said that the North must prove it is not engaged in terrorism before it will be removed from Washington’s blacklist.

“We want all countries in the list to be removed but we want them to be removed by showing us that they are no longer engaged in the practice that put them on the list,” Hill told reporters after arriving in Tokyo.

Taking North Korea off the terror list, long one of its key demands, was one of a series of economic and political concessions offered to the country to disable its nuclear reactor that produces plutonium for bombs. The list also includes Iran, Syria, Sudan and Cuba.