North Korea has approximately 10 nuclear warheads as of January 2016, a renowned research institute said in its annual report published on Monday.

The Stockholm International Peace Research Institute (SIPRI) estimated that North Korea has added two to four nuclear warheads to its stockpile from last year.

The report however added few specifics in terms of Pyongyang’s delivery systems for nuclear weapons.

“North Korea is estimated to have enough fissile material for approximately 10 nuclear warheads,” the press release from the institute reads. “However, it is unclear whether North Korea has produced or deployed operational weapons.”

The institute had judged