North Korea must prove it is not engaged in terrorism before it will be removed from Washington’s blacklist of states sponsoring terrorism, a top US diplomat said Friday.

US Assistant Secretary of State Christopher Hill said the United States was working with North Korean officials on the issue, as American experts prepared to start disabling the communist nation’s nuclear reactor.

“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. Japan is worried that the US will remove North Korea from the list despite what Tokyo sees as the North’s refusal to satisfactorily address the abductions of Japanese citizens in the 1970s and 80s. Hill said in Tokyo that the US wants to see progress on the abduction issue.

“I stressed to the North Koreans we want to see progress on this issue,” said Hill, who met with his North Korean counterpart, Vice Foreign Minister Kim Kye Gwan, in Beijing earlier this week.

“We don’t want a situation where denuclearisation is achieved while some relations among states are allowed to deteriorate,” Hill said after meeting with his Japanese counterpart, Kenichiro Sasae. Sasae said Hill assured him that the US will continue to support Japan on the issue.