North Korea has said it plans to increase the amount of plutonium it extracts for use in nuclear weapons, according to a US scholar.
The US has been monitoring activity at North Korean nuclear sites
Selig Harrison said North Korean officials had told him they would unload nuclear fuel rods from the Yongbyon reactor by the year's end.
Mr Harrison said Pyongyang wants "to use Yongbyon as leverage" to get bilateral talks with the US.
The US insists the nuclear issue can only be addressed in six-party talks.
Pyongyang walked out of multilateral negotiations with the US, China, Russia, Japan and South Korea late last year in protest at US financial sanctions.
It had agreed to enter the talks when offered aid and security guarantees in exchange for dismantling its nuclear programme.
International concern sparked by the North's recent missile tests has been mounting with speculation that it may be planning to test a nuclear bomb.
Selig Harrison told reporters in Beijing he had met several North Korean officials on a recent trip to the country, including the top nuclear negotiator, Kim Kye-gwan.
Mr Harrison is one of very few US academics with close contacts with the North Korean government.
He said Mr Kim had told him the "purpose of unloading the fuel was to obtain more plutonium for nuclear weapons".
He said he had been told the move was aimed at urging the US to meet North Korea's demand for bilateral talks.
The US believes Pyongyang could be capable of producing two or more bombs every year.
Intelligence reports of heightened activity at a suspected underground site in North Korea have prompted reports that Pyongyang might be planning a nuclear test.
Mr Harrison is quoted by the Associated Press news agency as saying he believes the North Korean leadership is still debating whether to conduct a test.