North Korea said on Tuesday it had made an important step in expanding its nuclear arsenal, venting frustration with Washington, which is still calibrating its response to Pyongyang’s request for bilateral talks.

Authoritarian North Korea, which is already estimated to have enough plutonium for as many as eight nuclear bombs, said it had reprocessed 8,000 fuel rods from its Yongbyon nuclear power plant. Experts estimate this could provide material for one or two more weapons.