TOKYO, March 25 (UPI) -- North Korea may be capable of producing nuclear warheads, a Japanese think tank stated Friday.
Tokyo's National Institute for Defense Studies said in its annual East Asian Strategic Overview report Pyongyang developed miniaturization capabilities under Kim Jong Un's direct orders, Jiji Press reported.
The report also stated the North is ramping up submarine-launched ballistic missile development, and if Pyongyang deploys SLBMs, its nuclear capabilities would make significant advancements.
Since Kim came to power, North Korean officials have been purged at increasing rates, the Japanese report stated.
"Fearpolitik through purges is strengthening the dictatorship," the report stated, according to South Korean news service Newsis.
The Japanese findings align with a growing concern in Washington that North Korea has made advancements in weapons miniaturization.
A number of U.S. officials told CNN they have reason to believe North Korea has "probably" a miniaturized nuclear warhead in its possession.
There have been no formal announcements on the issue in Washington, although North Korea has increasingly touted its nuclear weapons capabilities and has claimed it has nuclear-tipped ballistic missiles capable of hitting the continental United States.
Kim Jong Un is "determined to prove his doubters wrong," a U.S. official said.
Adm. William Gortney, head of the U.S. Northern Command, told Congress that it would be "prudent" to "assume [Kim] has the capability to miniaturize a nuclear weapons and put it on an ICBM."
Others are refraining from a definitive response and said assuming North Korea has the capability is not conclusive since they have "not demonstrated" its capacity, according to Pentagon Press Secretary Peter Cook.
Kim recently said Pyongyang had "successfully" tested a solid-fuel rocket engine and that the test is a stepping stone to developing a "ballistic rocket" that can "ruthlessly beat down hostile forces."