North Korea is expanding the operations of the Yongbyon nuclear site, renovating its 5 megawatt-electric (MWe) reactor to make plutonium for nuclear weapons and expanding the centrifuge plant, Institute for Science and International Security (ISIS) said in a recent report.

"The June 30th satellite imagery, combined with procurement data obtained by ISIS, suggests that North Korea is emphasizing the production of weapon-grade plutonium as well as enriched uranium for its nuclear weapons program," ISIS said in the report.

"Additionally, movement of material, a new piece of roofing, and several other renovations have been detected at the fuel fabrication and uranium centrifuge complex located in the southern part of the Yongbyon nuclear site."

Pyongyang is also constructing and possibly installing equipment at the experimental light water reactor (LWR) which would allow to produce "several times more plutonium than the 5 MWe reactor."

Pyongyang withdrew from the nuclear Nonproliferation Treaty in April 2003 and began developing its nuclear stockpile after a war in Iran, fearing an invasive regime change.

North Korea declared itself a nuclear power in 2005. In 2006, Pyongyang conducted its first nuclear test, followed by underground tests in 2009 and 2013. In response to North Korea's actions, the UN Security Council adopted a number of resolutions demanding Pyongyang to stop nuclear activities.

According to the Arms Control Association, North Korea currently has enough plutonium for approximately eight bombs.