NEW YORK • North Korea appears to be making new nuclear bomb fuel, satellite imagery shows, even as its leader Kim Jong Un has expressed willingness to negotiate atomic disarmament with US President Donald Trump.

Two separate teams of US analysts examining satellite images from January and last month have concluded that North Korea's reactor in Yongbyon - which had appeared to be dormant - is making plutonium, which is a principal fuel for nuclear arms.

In a report last week, one of the teams at 38 North, a research institute at Johns Hopkins University's School of Advanced International Studies, said rising plumes of steam from the reactor complex, as well as melted river ice nearby, suggested that "the reactor is operating again" to make plutonium for Pyongyang's nuclear weapons programme.

The team of analysts at 38 North includes Mr Frank V. Pabian, a former satellite image analyst at the Los Alamos National Laboratory in New Mexico, the birthplace of the bomb.

The signs of nuclear activity coincided with the North's string of diplomatic overtures to South Korea and the United States.

The overtures began with Mr Kim's conciliatory message towards South Korea in his New Year's Day address, and intensified last month during the Winter Olympic Games in Pyeongchang, South Korea.

North Korea's diplomacy accelerated last week, punctuated by Mr Kim's meetings with South Korean envoys, and the announcement that he and Mr Trump - leaders known for their bombastic threats - would meet in May to discuss denuclearising the Korean peninsula.

Nuclear experts say a core of irradiated fuel from the Yongbyon reactor can be processed to make between two and three nuclear weapons... Conservative estimates made in the past year or so put North Korea's overall atomic fuel production as sufficient to make between 20 and 25 weapons.

Nuclear experts say a core of irradiated fuel from the Yongbyon reactor can be processed to make between two and three nuclear weapons. North Korea began its nuclear programme with plutonium, and later expanded into uranium.

Conservative estimates made in the past year or so put North Korea's overall atomic fuel production as sufficient to make between 20 and 25 weapons.

The 38 North team identified plumes of steam rising from the reactor in satellite images obtained between Feb 17 and 25 - the day the Winter Olympics closing ceremony was held.

The other team, at the Institute for Science and International Security - a private group in Washington that tracks nuclear arms - came to similar conclusions about the North's nuclear activity.

Three analysts studied satellite images taken between Jan 17 and 30 and discussed them in two reports, the first on Feb 2 and the second on Feb 13, as the Games were in full swing. North Korea, the second analyst team said, "may be on the verge of expanding its stock of plutonium for nuclear weapons".

All the images, evidence and analyses of the nuclear activity come as North Korea's programme for missile development has entered an unusual period of inactivity. The nation has fired no missiles this year, compared with 20 known launches last year.

NYTIMES