U.S. Forces Korea Commander Curtis Scaparrotti said Friday that North Korea was thought to have the capability to miniaturize a nuclear warhead. 

His remarks escalated concerns that Pyongyang is getting close to weaponizing its nuclear capability by placing it atop a missile, which could pose a threat not only to South Korea but also to the U.S. 

The North conducted nuclear tests in 2006, 2009 and last year, and experts say Pyongyang might have accumulated the technology to build nuclear warheads small enough to mount at least on some of its ballistic missiles. 

Pyongyang has already claimed that it has succeeded in “lightening and miniaturizing” nuclear warheads. 

Scaparrotti’s remarks on the North’s nuclear weapons capability came a day after Seoul and Washington agreed to delay the transfer of wartime operational control, previously set for December 2015, in light of the North’s evolving nuclear and missile threats.