The United States believes North Korea has already succeeded in making some nuclear weapons small enough to fit atop missiles, a top American military official said Thursday.



"We know North Korea's ambitions in terms of their demonstrated cyber, their ambitions for nuclear weapons, the tests that have already occurred. And we think they already miniaturized some of this capability," Adm. Cecil Haney, commander of the U.S. Strategic Command, said during a Senate Armed Services Committee hearing.



In October, Gen. Curtis Scaparrotti, commander of U.S. Forces Korea, said that as USFK commander, he assumes the North has the capabilities to miniaturize nuclear warheads and that the country has "the technology to potentially actually deliver what they say they have."



Early this year, South Korea's Defense Ministry said in its "white paper" report that it believes the communist nation has reached a "significant" point in efforts to mastering the warhead miniaturization technology.



The U.S. Department of Defense later said, however, that there is no evidence the North has mastered the miniaturization technology, and what Scaparrotti said was that it is prudent for him as a commander to prepare for such a contingency.



North Korea has conducted three underground nuclear tests so far, in 2006, 2009 and 2013. The country has also conducted a series of long-range missile or rocket launches since 1998. In its latest launch in late 2012, the North succeeded in putting a satellite into orbit.



Experts have warned that it is only a matter of time until the North develops nuclear-tipped missiles.



Joel Wit, editor of the website 38 North, and David Albright, head of the Institute for Science and International Security, also said that they believe the North can miniaturize warheads sufficiently to place them on the Nodong medium-range ballistic missiles.



The two experts on North Korea's nuclear program made the claim in an article while rejecting criticism of their surprising estimate announced late last month that the North's nuclear arsenal could expand to 100 weapons by 2020. (Yonhap)